756 MR. c. TATE REGAN ON [June 19, 



of them branched. Some of the radials of the pectoral fin articu- 

 lated directly to the pectoral arch between mesopterygium and 

 metapterygium. Mixopterygia with 2 proximal axial segments, 

 with the marginal cartilages long, the dorsal one extending nearly 

 to the proximal end of the axial cartilage and the ventral one 

 not quite so far, with 5 or 6 terminal pieces and 1 to 3 dorsal 

 covering pieces, and with the glandular body restricted to the 

 glandular sac proper. Vertebral column with the secondary 

 calcification much as in the preceding family, but with dorsal and 

 ventral rays most developed. 



Principal genera : Rata, Psammohatis, Sympterygta. The 

 former dates from the Cretaceous ; the Cretaceous genus Cyclohatis 

 is allied to Sympterygia^, 



The Raiidse are clearly modified from Rhinobatidse of the type 

 of Rhinohatus, to which they bear a considerable resemblance. In 

 the dentition and in the presence of two longitudinal folds on the 

 side of the tail similar to the preceding family, but in the greater 

 development of the pectorals and the degeneration of the vertical 

 fins of a more specialised type. Psammohatis is peculiar in lacking 

 a rostral prolongation of the cranium. 



Family 3. DASYBATiDiE. 



Prseorbital cartilages articulated to the propterygia. Dorsal fin 

 absent or else a single small fin situated near the root of the 

 tail ; caudal fin present or not ; pectoral fins extending to the 

 extremity of the snout ; pelvics not notched. Often one or more 

 strong serrated spines on the tail, behind the dorsal fin if this be 

 present. Basalia of the dorsal fin more deeply imbedded anteriorly 

 than posteriorly ; radials branched, extending to the free edge of 

 the fin. Pectoral mesopterygium extending the whole of the 

 distance between propterygium and metapterygium, sometimes 

 segmented into 2 or 3 pieces. Mixopterygia with 2 proximal 

 axial segments, with marginal cartilages of moderate length and 

 distal in position, with 2 terminal pieces and 1 or 2 ventral 

 covering pieces, and with the glandular body extending nearly to 

 the distal end of the appendage. Yertebi-al column with secondary 

 calcification much as in the Rhinobatidse. 



Several of the recent genera as well as the extinct Xiphotrygon 

 occur in the Eocene. The Cretaceous Ptychoclus appears to be 

 intermediate between Dasyhatis and Myliohatis. 



The lateral tail-folds characteristic of the preceding families 

 are usually absent, but vertical folds may be developed. A 

 cartilaginous rostrum is absent. Dissection of a specimen of 

 Myliohatis aquila shows that the generally accepted idea that the 

 pectoral fins are interrupted, leaving the sides of the head free 

 and reappearing at the extremity of the snout, is erroneous. The 

 propterygia have exactly the same form and extent as in Dasyhatis 



. * In Sympteri/gia the pelvis has well-developed prsppubic processes, as in Cyclobatis. 

 In the latter the enlarged anterior pelvic radial has been mistaken for a lateral 

 process of the pelvis. 



