The uniformly flattened cloacal area was appar- 

 ent as an unusual feature of the specimens only 

 when they were fresh or were preserved in forma- 

 lin. After transfer to alcohol this flattening dis- 

 appeared. 



The presence of an adult male in the haul also 

 revealed the remarkable difference in tooth size 

 and shape (fig. 10) between adult males and fe- 

 males. Although later collections produced an- 

 other adult male from near Key West, the only 

 immature specimens seen thus far have been fe- 

 males, so it has not been determined when the tooth 

 dimorphism first appears. 



The teeth in the six specimens examined are in 

 24 + + 24/19 + + 19 to 29 + + 29/22 + + 21 

 rows with no teeth at the symphysis in either jaw. 

 The teeth of the females are generally tricuspid 

 in the central portion of the jaws but have five, 

 seven, or nine cusps toward the angles of the jaws. 

 The number and shape of the teeth of females of 

 the series described here are about as described for 

 A. riveri by Bigelow and Schroeder (1944, 1948). 

 Using the definition of series of teeth given earlier 

 in this paper, however, the number of functional 

 series in riveri is five or six. The tooth arrange- 

 ment, as in other Apristurus or, for that matter, in 

 all scyliorhinids, is in alternate series with series 



defined as teeth arranged along a single line paral- 

 lel with the axis of the jaw. This arrangement 

 gives the appearance of diagonal rows (see fig. 11) . 

 It may be described also as Bigelow and Schroeder 

 (1944) have done as an arrangement in quincunx. 



In dealing with somewhat larger series than 

 were available to Bigelow and Schroeder, some 

 difficulties have appeared in the use of distances 

 between gill openings and angles formed by the 

 labial grooves as means for differentiating species, 

 because of greater variation in the larger series. 

 Among western Atlantic species the narrower 

 head of riveri seems the most outstanding and re- 

 liable criterion for quick identification. The com- 

 paratively narrower head is shown quite clearly 

 in figure 27. In riveri the band of pores on the 

 underside of the snout is consistently narrower 

 than in other western Atlantic species, generally 

 being composed of about four rows of pores in- 

 stead of eight or more. 



The claspers of the adult males are rather short, 

 reaching about 2.3 percent of total length beyond 

 the tips of the pelvic fins, and quite stout. There 

 are no hooks. The clasper siphons are also rela- 

 tively short, extending only about 10 mm. in ad- 

 vance of the origin of the pelvics. 



Figure 24. — A, Apristurus riveri Bigelow and Schroeder, drawn from a 400-mm. female from M/V Oregon 

 station 3586; B, Apristurus laurussoni (Saemundsson), drawn from a 540-mm. male, MCZ 38406. 



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U.S. FISH AND WILDLIFE SERVICE 



