by william a. haswell, m.a,, b sc. 117 



Rajid^:. 



The articular surface for the hyo-niandibular is borne on a 

 prominent process of the postero-lateral region of the skull. 

 The ethmoidal region is produced into an undivided rostrum. 

 The hyoid arch is connected with the base of the hyo-mandibular. 

 There is only one branchial copula ; the copularia are not amal- 

 gamated with it it, The pectoral arch articulates directly with the 

 spinal column. The propterygvu/m articulates with the skull by 

 means of an ant-orbital cartilage ; the pectoral fin is interrupted 

 in front, with no detached cephalic fin. Short ribs are present. 

 Some of the rays of the pectoral fin articulate with the shoulder- 

 girdle. 



TRYGONIDiE. 



There is no distinct rostral prolongation of the skull. The 

 articular surface for the hyo-mandibular is elongated antero-pos- 

 terioi'ly ; it is situated near the base of the skull, and not borne on a 

 prominent process. The branchial copula is coalescent with the 

 copularia. The hyoid arch sometimes articulates with the proximal 

 extremity of the hyo-mandibular, sometimes with the cranium 

 directly. The pectoral fins are continuous in front ; the pectoral 

 arch articulates with the spinal column. None of the rays of the 

 pectoral fin articulate directly with the pectoral girdle. There 

 are no ribs. 



Myliobatil\e. 



The cranium is elevated in front. There is no distinct rostrum. 

 The articular surface for the hyo-mandibular is a tolerably deep 

 hollow, situated close to the base of the skull, but not so much 

 elongated as in most other Rays. The branchial copularia coalesce 

 with the copulae. The hyoid arch is not related to the hyo- 

 mandibular nor to the skull, but articulates with the base of the 

 first branchial arch, which articulates with the skull behind the 

 hyo-mandibular. The pectoral fins unite in front of the skull ; 

 the pectoral arch articulates with the spinal column. There are 

 no ribs. 



