Fishes of the IV es tern North Atlantic 5 



However, one group, the Sawfishes (Pristoidea), are shark-like in general appear- 

 ance, though they are grouped among the batoids because of the relationship of the 

 pectorals to the gills and because of the absence of upper eyelids, as well as on skeletal 

 grounds. And most of the Guitarfishes (families Rhynchobatidae and Rhinobatidae) 

 are Intermediate in form, between shark-like and batoid-like. 



Some batoids have no dorsal fin, whereas others have one or two, in which case 

 the first dorsal (when there are two) varies in position from over the pelvics to far back 

 on the tail. Some have a distinct caudal fin, which others lack. In all fins of some species 

 the radial cartilages are supplemented distally (as in Sharks) by much more numerous 

 fine horny rays (ceratotrichia) in double series, their inner ends embracing the outer 

 ends of the cartilaginous radials ; in others the unpaired fins have these horny rays 

 whereas the pectoral and pelvic fins, in which the cartilaginous radials run out nearly 

 or quite to the margin, do not ; in still others neither the unpaired nor paired fins have 

 horny rays. The spiracles are larger than those of most Sharks and are situated on top 

 of the head in all cases ; the rudimentary spiracular gill filaments are better developed 

 than in Sharks, as is also the so-called spiracular valve, a stiff concentric fold of con- 

 nective tissue on the anterior margin of the spiracle which is supported by a strong 

 cartilage fixed at each end. The eyes are well developed in most, though degenerate 

 in a few. All have five pairs of gill openings. 



The skins of some are naked while those of others are variously armed with thorns, 

 tubercles or prickles ; the tails of some bear large saw-edged spines. The teeth vary 

 from thorn-like to rounded or platelike (none have the blade-like dentition so charac- 

 teristic of many Sharks), placed either in bands, in transverse rows, or in pavement 

 or mosaic arrangement. The nostrils are connected with the mouth in some cases but 

 are entirely separate from it in others. In one family, the Sawfishes, the snout is pro- 

 duced as a long flat blade supported by the rostral cartilages in the form of five or more 

 calcified tubes (described on p. 16) and is armed along either edge with a single series 

 of strong tooth-like structures, much as in the Saw Sharks (Pristiophoroidea). The heart 

 valves are in two to seven rows.^ 



Some members of the order have electric organs more or less well developed, 

 but none have luminescent organs so far as is known. 



The vertebral column is completely segmented throughout its length in all species, 

 with the centra fully differentiated and the axial canal so greatly constricted in its passage 

 through them that the notochord is wholly or almost wholly obliterated there. Secondary 

 calcifications of the vertebral centra in the form of radiating lamellae are described as 

 growing inward toward the primary calcified double cone. 



The Batoidei in which the anatomy has been studied, including the Sawfishes, 

 differ from all modern Sharks in the attachment of the pectorals to the sides of the 

 head, in the lack of a free upper eyelid, in the better developed spiracles, in the ventral 



5. See Garman (Mem. Harv. Mus. comp. Zool., j6, 1913: pi. 56, figs. 7-10, pi. 57, figs. 1-6) for illustrations from 

 original dissections of the heart valves of various batoids; see White (Bull. Amer. Mus. nat. Hist., ^4, 1937: 87, 91) 

 for a general discussion of their significance in classification and for tabulations of their numbers in various Sharks 

 and batoids. 



