Fishes of the IV es tern Nortfi Atlantic 135 



siderable distance at the anterior end*^ for the reception of the sperm and at the terminal 

 end for its emergence.' Along the midsector of the groove, however, one of the edges 

 overlaps the other, the two being held so closely in contact by the scroll-like form of the 

 supporting cartilages that the channel is to all intents a closed tube although its edges 

 are not actually fused. The supporting structures consist of: (a) two or more short basal 

 joints that connect with the tip of the metapterygial cartilage of the pelvic fin; (b) an 

 axial cartilage extending throughout most of the length of the clasper; (c) two narrow 

 lateral cartilages (right and left) that develop along the outer face of the axial cartilage, 

 to enclose the seminal groove as maturity approaches; and (d) three or more terminal 

 cartilages, more or less movable, which vary in number and shape from species to 

 species and which are often extremely complex; one or more of them may have spine- 

 like or blade-like tips or edges. These terminal cartilages, which model the overlying 

 tissues, often throw open the terminal section of the seminal channel, thus exposing 

 the inner walls and a complex pattern of ridges and pockets; undoubtedly this is a func- 

 tion associated with copulation. The function of the cutting structures has been the 

 subject of speculation into which we need not enter here. 



Genera. One of the species that belongs here is set apart from all others, indeed 

 from all other known batoids, by the conspicuous fact that several of the middle rays 

 of each of its pectorals are elongated so as to form a narrow spatulate lobe (Fig. 77). 

 It formed the basis of the genus Dactylobatus Bean and Weed 1909, which commonly 

 has been accepted. The remaining members of the family, i. e., those of normal skate- 

 like outlines, are divisible into two rather sharply defined groups according to the 

 structure of the pelvics. 



A. The margins of the pelvics are so deeply notched as to give the anterior division 

 the form of a slender subcylindrical limb which is entirely separate externally from the 

 posterior division of the fin and which arises independently from the lower surface of 

 the disc some distance in from the edge of the latter. This specialization is also accom- 

 panied by interesting skeletal modifications (described on p. 314). Four species are 

 known within this group, all of them referable to the genus Cruriraja Bigelow and 

 Schroeder 1948 (p. 313). 



B. The anterior and posterior portions of the pelvics are continuous externally 

 one with the other, as is usual among batoids, though the outer margin may be so 

 deeply concave that the fin is definitely bilobed. This group includes all of the numerous 

 members of the family that remain. Its representatives can be distributed among three 

 subdivisions: 



1. Those in which the rostral projection from the front of the cranium (rostral 

 cartilage) extends at least as far as the tips of the anterior rays of the pectoral fins and 

 nearly to the extreme tip of the snout. 



2. Those in which the rostral projection is so reduced that its tip falls short of 

 the tips of the anterior rays of the pectoral fins, and shorter still of the tip of the snout. 



3. Those in which there is no cartilaginous rostral projection from the cranium, 



6. The "apopyle" of Leigh-Sharpe. 7. The "hypopyle" of Leigh-Sharpe. 



