catulus) by Leigh-Sharpe (1920) and apparently 

 is a feature common to all galeoid sharks but not to 

 sharks of other suborders. 



Shape of body and fins 



The caudal axis in the family Scyliorhinidae is 

 little elevated and, excepting adults of Scyliorhi- 

 nus, the overall shape of western Atlantic species 

 is slender. One genus, Schroederichthys, has a 

 very elongate postpelvic trunk region. 



The length of the body cavity relative to the 

 overall size of the fish (volume) differs consider- 

 ably in the four genera found in the tropical and 

 northern Atlantic. This difference is reflected in 

 the size of the liver and it appears likely that 

 with sufficient material for study it would be found 

 that liver characteristics would be useful as tax- 

 onomic criteria. The general shape of the liver 

 is shown in figure 5. 



A series of Pacific Apristurus brunneus ex- 

 amined in comparison with Apristurus riveri from 

 the Atlantic show some apparently constant dif- 

 ferences in liver shape. In A. brunneus the liver 

 is larger and in most specimens the right and left 

 posterior lobes are united for most of their length, 



excepting only that part just anterior to and ex- 

 tending past the cloaca. In A. brunneus the liver 

 almost completely covers the visceral cavity when 

 viewed from the ventral aspect. Only the falci- 

 form ligament and the rectum are visible in addi- 

 tion to the liver when the body cavity is opened 

 vent-rally. Thus it would seem from casual inspec- 

 tion that large ripe eggs from the ovary located 

 under the liver when viewed from the ventral as- 

 pect (only right ovary functional in scyliorhinids) 

 would have to make a remarkably long or tortuous 

 journey to reach the opening of the oviducts. 



It may be significant in indicating possible deri- 

 vation of the orectolobids which have quite short 

 snouts with reduced or absent rostral cartilages, 

 that western Atlantic ScyUorhinus and Halae- 

 lurus have relatively short snouts, Schroederich- 

 thys has a moderately short snout, but both Galeus 

 and Apristurus are long-snouted. Associated with 

 the long snouts of Galeus and Apristurus is the 

 comparatively greater prominence of the external 

 pores for the Ampullae of Lorenzini. The exten- 

 sive pore system of the Ampullae of Lorenzini in 

 Apristurus may be associated with its habitat 



Fioure 5. — Diagrams of the arrangement of visceral organs showing liver shai>es (stippled areas) in repre- 

 sentatives of four western Atlantic genera: A, ScyUorhinus retifer; B, Galeus arac; C, Schroederichthys 

 maculatus; and D, Apristurus riveri. 



REVIEW OF WESTERN ATLANTIC CAT SHARKS 589 



793-358 O — «6 5 



