THE AISTOPODOUS MICROSAURIAN FAMILY PTYONIID^. I45 



tain characterization. The fore Hmbs are indicated by a humerus. There were 

 possibly from 75 to 100 vertebrae in the entire column. The animal was exclusively 

 adapted to life in the water and was, without doubt, an excellent swimmer. There 

 are preserved in one specimen portions of what seem to be hyobranchial elements. 



Measurements of CEstocephalus remex Cope. 



mm. mm. 



Length of entire caudal series 195 Length of mandibular dental scries 24 



Width at ninth vertebra 21 Depth of mandible at middle 5 



Width at thirty-sixth vertebra 2 Nine teeth in 5 



Length of four phalanges in place 14 Length of longer teeth 2 



Expanse of fan of proximal caudal 18.5 I^ength of first hcemal branchial 6 



Length of ilium 1 1.5 Length of sixth vertebra from skull 7 



Length of femur 1 1.5 Width of centrum 3 



Length of tibia 7 



CEstocephalus rectidens Cope. 



Cope, Trans. Amer. Phil. Soc, p. 268, Apr., 1874. 



Cope, Geol. Surv. Ohio, ii, pt. 11, p. 386, pi. xxvii, fig. 3, 1875. 



Type: Specimen No. 9033, American Museum of Natural History, collection 

 of J. S. Newberry. 



Horizon and locality: Linton, Ohio, Coal Measiires. 



The species is indicated by a left dentary bone, with its teeth and external sur- 

 face preserved. The latter is nearly smooth and without sculpture. The outer 

 face is convex, and the general form is slender, but not curved upward at the extrem- 

 ity. The extremity of the dentary does not show any evidences of teeth. Teeth 

 straight and conic, apex acute, non-plicated. 



Cope also associated with this species a portion of a caudal series, consisting 

 of 25 vertebrae. The centra are elongate and expanded at the extremities. The 

 neural arches have a close union. The neural and haemal spines are fan-shaped and 

 striated. The bases are quite narrow. 



Measurements of CEstoceph.\lus rectidens Cope. 



mm. mm. 



Length of dentary 22 Length of 3 centra of the caudal series 8.6 



Length of tooth line 15.2 Extent of neural and haemal spines 8.7 



Depth of dentary at last tooth 2.7 



Genus THYRSIDIUM Cope, 1875. 

 Cope, Geol. Surv. Ohio, 11, pt. 11, p. 365, pi. xxxi, fig. 2, 1875. 



Type: Thyrsiditim fasciculate Cope. 



Established on a species which presents its principal peculiarities in the struc- 

 ture of the vertebrae. Two specimens present inferior views of the spinal column, 

 showing that the genus possesses, like Siren, enlarged diapophyses, but they are 

 peculiar in their fan-like form. They resemble slightly the neural spines of the 

 caudals of Ptyonius, but are present on the dorsal vertebrae. Whether the caudals 

 of the present species possess ornamented neural spines the specimens do not indi- 

 cate. The abdomen is protected by the usual hair-like rods arranged en chevron, 

 the angle directed forwards. No indications of limbs can be discovered on the 

 blocks. 



