This family is distinguished by the formula
- 3 1 4 3
- ———,
- 3 1 4 3
by the incisors, canine and premolar 1 all being of subequal size, by all the teeth being brachydont, and by the crescents of the lower premolars and molars being modified. On these lower premolars and molars the anterior crescent is longer than the posterior, and the short posterior crescent on the exterior of the tooth; so that its anterior horn, instead of uniting with the posterior horn of the anterior crescent, comes in back to about the middle of the anterior crescent. Then the pillar, which in the other families is situated in the posterior crescent, is opposite the posterior horn of the posterior crescent. The small animals which represent this family are rare in the Deseado beds, much more abundant in the Casamayor. The family seems to have died out in the Deseado as no forms are referred to it in later epochs. We found no specimens belonging to the family; but to make this discussion complete, I will give a digest of Ameghino’s descriptions, with reproductions of such figures as he has given. All of the genera and species are based on very fragmentary material.
The genera assigned to the family are Trimerostephanos, Pleurocoelodon, Lophocoelus and Henricofilholia.
Trimerostephanos Ameghino
Trimerostephanos Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p. 646.
Trimerostephanos Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 483.
This genus is based on upper and lower teeth, and distinguished by the premolars and molars having a weak style on the anterior corner, and by the anterior lobe being considerably larger than the posterior. Four species have been described.
T. scabrus Amegh., loc. cit. for genus.
This is the type species, originally based on the third lower molar, to which was later added, upper premolar 4 and the molars, and lower molar 2. The following measurements are given:
| Measurements | |||
|---|---|---|---|
| Upper premolar 4, | length | 15 mm., | width 21 mm. |
| Upper molar 2, | length | 31 mm. | |
| Upper molar 3, | length | 35 mm. | |
| Lower molar 2, | length | 20 mm. | |
| Lower molar 3, | length | 29 mm. | |
Fig. 87. T. scabrus—natural size;
A, upper premolar 4;
B, lower molars 1 and 2.
T. scalaris Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 483, is based on lower pm. 2 to m. 2, a somewhat smaller species than the preceding, the series as given measuring 53 mm.
Fig. 88. T. scalaris, premolar 2 to molar 2—
natural size.
T. angustus Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 484.
This species is described without a figure, as smaller than T. scalaris, pm. 2 to m. 2 being 59 mm. The mandible is also slenderer.
T. biconus Amegh., 1897, Bol. Inst. Geog. Argen., t. 18. p. 484.
This species is based on two lower premolars, said to be the same size as T. angustus, but with the pillar larger.
Pleurocoelodon Ameghino
Pleurocoelodon, Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p. 645.
Pleurocoelodon, Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 484.
This genus is distinguished by the absence of the style on the anterior external margin of the upper molars, instead of which the external face is excavated medianly. Two species are described, based on isolated upper teeth.
Fig. 89. P. wingei—natural size; A, first molar;
B, third molar.
P. wingei Ameghino
P. wingei Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p. 645.
P. wingei Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 485.
This species is founded on a couple of isolated molars, probably belonging to the same individual. The following measurements are given:
| Upper molar 1, | length | 22 mm., | width | 26 mm. |
| Upper molar 3, | length | 24 mm., | width | 29 mm. |
P. cingulatus Amegh., loc. cit. above, is based on an incomplete upper molar, probably the second, which is distinguished by having the internal cingulum excessively developed. It measures 30 mm. in length.
Lophocoelus Ameghino
Lophocoelus Amegh., 1904, Anal. Soc. Cient., Rep. Argen., t. 58, p. 245.
Lophocoelus Amegh., 1904, Anal. Mus. Nac., ser. 3, t. 3, p. 352.
The genus is founded on a single upper third molar from Mazaredo, which is distinguished by a feeble style on the external face, by the anterior lobe being obliquely placed, and by the presence of a small secondary bay on the posterior side of the great internal basin.
L. macrostomus Amegh., loc. cit. above.
This species is the only one described, and has the generic features, the upper m. 3 being 21 mm. long, by 25 mm. wide.
Henricofilholia Ameghino
Henricofilholia Amegh., 1901, Bol. Acad. Nac. Cordoba, t. 16, p. 404.
The type species is H. cingulata, based on a single upper molar. In general the upper molars are similar to those of Leontinia, but more brachydont, and with the internal cingulum well developed and tending to be crenulated. Four species have been made, all based on isolated upper molars.
Henricofilholia cingulata Ameghino
- H. (? Parastropotherium) cingulata Amegh., Bol. Inst. Geog. Argen., t. 15, p. 640.
- H. (? Parastropotherium) cingulata Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 450.
- H. cingulata Amegh., 1901, Bol. Acad. Nac. Cienc. Cordoba, t. 16, p. 404.
Fig. 90. H. cingulata,
upper molar 1—
natural size,
after Ameghino.
This is based on an upper molar 1 of which I reproduce Ameghino’s figure. It measures 28 mm. long by 29 mm. wide.
H. lustrata Amegh., 1901, Bol. Acad. Cienc. Cordoba, t. 16, p. 405.
This species is smaller than the preceding, and is based on an upper molar 1 and a last lower molar. The measurements are as follows:
| Upper molar 1, | length | 25 mm., | width | 25 mm. |
| Lower molar 3, | length | 25 mm., | width | 12 mm. |
Fig. 91. H, inaequilatera, upper molars 3 and 4—
natural
size, after Ameghino.
H. inaequilatera Amegh. loc. cit. above.
This species is larger than the preceding with the internal cingulum more developed. Upper molar 2 measures 30 mm. long by 29 mm. wide.
H. circumdata Amegh., loc. cit. above.
This is a still larger type, with the internal cingulum enormously developed. Upper molar 1 measures 42 mm. long by 36 mm. wide.