which is in comparatively deeper water than any 

 of the other cat sharks. Pineal windows were not 

 seen in the specimens of Apristurus or any other 

 cat sharks examined. Among sharks, these are 

 consistently present in the squaloid genus 

 Etmopterus, members of which are black. 

 Dermal denticles 



The size, arrangement, and structure of dermal 

 denticles are often quite useful characters for prac- 

 tical problems in identification of sharks. Ordi- 

 narily the typical dermal denticles used in descrip- 

 tive accounts of species are those from a lateral 

 surface near the first dorsal fin but below the mid- 

 dorsal line. Here, unless some specific location 

 is indicated, denticle descriptions are from den- 

 ticles taken at a point about halfway along a line 

 between the axil of the pectoral fin and the origin 

 of the first dorsal fin. In some instances, differ- 

 ences in the denticle structure are the most reliable 

 and definite, means of determining species. For 

 example, Squalus blainvillei is readily distin- 

 guished from Squalus cubensis by great differences 

 in denticle shapes. Among scyliorhinids of the 

 western Atlantic, denticle differences are either 

 less well marked or need qualification as to loca- 

 tion or as to the size or age of the specimens in- 

 volved in comparisons. 



In Scyliorhinus retifer the denticles increase in 

 size as the shark becomes larger and the denticles 

 change somewhat in shape. In some sharks it is 

 evident that the number of denticles increases as 

 the shark grows large, but in the series of S. retifer 

 examined, positive evidence of an increase in the 

 number of denticles with increasing size was not 

 apparent in a cursory examination. The general 

 aspect of a section of skin surface with denticles is 

 shown in figure 6. 



In Scyliorhinus retifer denticle shapes on differ- 

 ent parts of the body vary and the variation fol- 







Figure (>. — Dermal denticles from a series of female 

 Scyliorhinus retifer from the Gulf of Mexico. I/eft 

 from a specimen 1 T.I mm., center from a 295-mm. speci- 

 men, and right from a 465-mm. specimen. Camera 

 lucida drawings to the scale indicated. 



lows a pattern more or less characteristic of all 

 galeoid sharks. On the ventral surfaces the denti- 

 cles have much less prominent ridges and the lat- 

 eral points are generally absent. On leading edges 

 of fins the denticles are usually smoother and flat- 

 tened so that there are no projecting points. On 

 the head and especially those parts of the head 

 used sometimes for bumping objects, the denticles 

 are somewhat shorter with thicker edges or points. 



Denticles of Gal-ens and Apristurus follow this 

 plan to a less marked degree. The denticles of 

 ventral surfaces are about the same shape as those 

 of the dorsal surfaces, but their construction is 

 lighter. 



Specialized dermal denticles forming a crest 

 along the upper margin of the caudal fin are found 

 on all species of the genus Galeus, varying slightly 

 among species but probably not sufficiently to be 

 used in practical field identification. The genus 

 Figaro Whitley has been described from Austra- 

 lian waters and differs in having the specialized 

 scales on both the upper and lower margins of the 

 caudal fin. The eastern Pacific genus Parniaturus, 

 quite unlike Galeus in many respects, has a denticle 

 crest on the upper caudal fin margin. 



Although not having a definite crest, Apristurus 

 profumdorwm has several rows of compactly ar- 

 ranged, imbricate denticles along the upper mar- 

 gin of the caudal fin. The body and sides of the 

 fins in that species are quite sparsely clothed with 

 denticles which are nearly erect. 



The young of Scyliorhinus canicuhis and S. 

 stellaris have a series of enlarged scales, one series 

 on each side of the middorsal line extending from 

 the shoulder area back to the first dorsal fin. Ac- 

 cording to Ford (1921), these scales are visible in 

 embryos of S. caniculus taken at Plymouth, Eng- 

 land, when the embryos are 44 mm. long. They 

 persist for a short time after hatching, but similar 

 scales are present on S. stellaris and may still re- 

 main in place until the sharks are over a foot long. 



Enlarged scales are present on an embryo (fig. 

 8) presumed to be S. retifer. They are not visible 

 in specimens of 150 mm. or more, but on specimens 

 of newly hatched S. retifer they are represented 

 sometimes by a series of scars. Enlarged denticles 

 in a similar position but widely spaced are present 

 in Halaebwrus from Chile, usually surrounded by 

 a ring of somewhat modified smaller denticles. 

 Series of enlarged denticles are present on both 



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