CHELONIIDE. 209 
the stapedial rod. Choanz placed on the line joining the centers of the orbits; the nasal 
passages underfloored by plates from the vomer and the palatines. Neck short, head not 
retractile. Carapace heart-shaped, excavated in front for the neck and for the fore limbs: 
often with costo-peripheral fontanels. Plastron loosely and ligamentously joined to the cara- 
pace; usually with median and lateral fontanels. Entoplastron small and lance- shaped. 
Limbs unfitted for locomotion on the land; converted into paddles for swimming; the anterior 
the more powerful. Humerus straightened and flattened; with the head nearly in the axis 
of the bone and with the ulnar al radial processes nearly in the plane of the distal end; 
the radial process below and free from the head. Second to fifth fingers elongated, the phalanges 
without condyles; and all bound together in the skin and muscles. Cee I or 2. 
At the present day the Cheloniide are represented by probably 4 genera (Eretmochelys, 
Colpochelys, Caretta, and Chelonia) and 5 or 6 species. Most, if not all, of these species 
enjoy a wide distribution, being found in all tropical and subtropical seas. All are seafaring 
animals, coming on the land only to deposit their eggs. They are mostly carnivorous in their 
food habits, but Chelonia feeds on vegetation. ; 
If Allopleuron hoffmanni, of Bolland: belongs to this family, as usually supposed, the 
family history extends backward to Upper Cretaceous times. Well- preserved remains of 
sea-turtles belonging to the divisions of the Tertiary are not common. In America we have 
a few species which are here assigned to the family with some doubt; such as those of Peri- 
trestus of the Upper Cretaceous of New Jersey and Georgia and Lembonax of the Eocene of 
New Jersey. It can hardly be doubted that Syllomus crispatus of the Miocene of Virginia 
belongs to the family; while it is probable that the species here called Procol pochelys ee 
and Chelonia parvitecta are also true Chelonidz. All of these are, however, imperfectly 
known. In Europe the known Tertiary forms are hardly more numerous or better known, 
Allopleuron hojjmann: is greatly specialized in some respects. Especially is its carapace 
much reduced. It is improbable that from it have been derived the modern Chelonide. 
It is more likely that the latter have descended from some Upper Cretaceous ancestor not 
distant from Toxochelys. The ancestors of Allopleuron must have become sea-turtles long 
before the Upper Cretaceous—consequently long anterior to the time when the ancestors 
of our modern Cheloniidz could be called sea-turtles. It is therefore probable that 4/lo- 
pleuron really belongs to a family distinct from the Chelomiude. 
Key to GENERA HERE DESCRIBED. 
A. First costal articulating with peripherals. Shell coarsely sculptured as in some 
Mito myChidusiem see tia sac Soci omit ieee = agstrie. vie sicfrs got Estws Sela vette ey Peritrestus 
AA. Costal plates articulating to peripherals and sculptured... ....... veeeeeeee.  Syllomus 
A! is he bones, so far as known, not articulating with peripherals and not sc ulptured. 
. Plastral bones without median digitations. .... eee eae See Lembonax 
aa. Plastral bones with median digitations. 
b. Some neurals in contact with three pairs of costals. Rib of first costal entering 
pit in third peripheral......... AEs eoe Uk eee ee ecceae Procol pochelys 
bb. Neurals in contact with two pairs of costals. Rib of first costal entering pit in 
itd! peripienall aiwtecs toe eu vies oe eee ess a ee es cre Chelonta 
Genus PERITRESIUS Cope. 
Carapace cordate, as in the Chelonide generally; the anterior peripherals suturally 
joined to the costals of the first pair; the posterior peripherals joined to costals by gomphosis 
of ribs only; a high dorsal keel; surface of carapace coarsely sculptured. 
Type: Chelone ornatus Leidy. 
In 1882 (Proc. Amer. Philos. Soc., xx, p. 144) and again in 1884 (Vert. Tert. Form. 
West, p. 112) Cope characterized this genus as having 9 pairs of costals, 2 anterior peripherals 
joined to the costals, and a high dorsal keel. It is now evident that he had derived his infor- 
mation from a carapace sent to him by Dr. George Little, at one time State Geologist of 
Georgia (Amer. Naturalist, 111, 1878, p. 129). 
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