Fishes of the Western North Atlantic 533 



Key to Genera 

 la. Five gill openings. Pm//opAor«i- Miiller and Henle, 1837. 



South Africa, Australia, Tasmania, Philippines, 

 Japan, Korea. 

 lb. Six gill openings. Pliotrema Reg^n, i()o6. 



South Africa. 

 Species. Pristiophorus includes three known species, Pliotrema only one.' 



Suborder SQUATINOIDEA 



Characters. No anal fin; 2 dorsal fins v/ithout spines; only 5 gill openings, all ante- 

 rior to origin of pectorals; snout not beak-like, without lateral teeth or cirri; teeth in front 

 of mouth essentially similar to those toward its corners; general form skate-like rather 

 than shark-like, with the trunk very much flattened dorso-ventrally and expanded later- 

 ally anterior to cloaca, but tapering thence rearward; eyes dorsal; anterior margins of 

 pectorals extending forward past gill openings* and partly concealing them; pelvics also 

 very broad, wing-like, their inner margins entirely separate posterior to cloaca; nostrils 

 separate from mouth ; spiracles present, dorsal ; eyes without nictitating fold or membrane; 

 vertebral column completely segmented throughout its length, its axial canal much con- 

 tracted in the region of the centra, which are well differentiated, with the notochord greatly 

 constricted segmentally in its passage through them; vertebral centra with 2 or more series 

 of concentric calcified lamellae; neural spines attached to dorsals;' rostral cartilage single, 

 very short; skull without antorbital processes or separate antorbital bars; upper jaw (pala- 

 toquadrate cartilage) articulated to hyomandibular bar, with a long transverse process that 

 is attached to the ethmoid region of the cranium by a ligament;" propterygial cartilage of 

 pectoral elongate, directed anteriorly, corresponding to forward expansion of the fin, but 

 bearing much fewer radials than the metapterygium;' pelvis curved rearward, corre- 

 sponding to the expanded pelvic fins; heart valves in 6 to 7 rows (an exceptionally large 

 number for sharks, but characteristic of skates and rays) .' Development ovoviviparous. 



Remarks. Although very skate-like in appearance, in number of heart valves, and in 

 some skeletal .characters, the squatinoids are usually classed with the sharks because they 

 have free eyelids, pectorals with anterior margins not attached to the sides of the head, 

 and gill openings that are not confined to the lower surface but extend up onto the sides 

 of the neck as well. 



Their method of swimming, also shark-like, is by a sculling motion of the tail, little 



3. For descriptions of the species of the two genera, with lists of references, see Fowler (Bull. U.S. nat. Mus., loo 



['ill '94' ■ i8o, 283). 

 4.. But not attached to sides of head. 5. Mivart, Trans, zool. Soc. Lend., to, 1879: pi. 77, fig. 5- 



6. For account and excellent illustration of the skull, see Gegenbaur (Unters Vergl. Anat. Wirbelt., 5, 1872: 190, 

 pi. II, fig. 2, pi. 12, fig. 4). 



7. Gegenbaur, Unters. Vergl. Anat. Wirbelt., 3, 1865: pi. 9, fig. 10. 



8. For account of the vertebrae and dermal denticles, see Hasse (Naturl. Syst. Elasm. besond. Theil, 1882: 126, 

 pi. 17, fig. i-io) } for heart valves, see Marples (Trans, roy. Soc. Edinb., 5* [3], 1936: 817). 



