if any, species enter relatively warmer areas or 

 shallow-water areas. The discovery by Poll 

 (1951) and Cadenat (1959) that the ovoviviparous 

 condition and the oviparous condition both occur 

 within a single genus (Galeus) points to the need 

 for much more observation on life histories of 

 catsharks. 



The order in which genera are taken up in this 

 paper is not intended to have any phylogenetic 

 implication. Galeus, Apristurus, and Schroede- 

 richthys, as far as these are known at present, are 

 quite compact groups of similar species and are 

 separable from each other and from other of the 

 world's scyliorhinid genera by many differences. 



The separation of Scyliorhimts from Halaslurus 

 and from some other genera of the Indo-Pacific 

 region has, in the past, been based primarily upon 

 differences in the arrangement of skin folds near 

 the mouth, by the presence or absence of nasoral 

 grooves, and by the relative development of anter- 

 ior and posterior nasal valves. Keys to genera and 

 also to species used by Garman (1913) and by 

 Fowler (1941) emphasize these characters. I have 

 given little descriptive space to them because they 

 appear to be of little use for determination of west- 



ern Atlantic species and also because they are some- 

 what variable in the specimens at hand. I have 

 also had some difficulty in understanding the ter- 

 minology. For example, Garman (1913) states 

 that nasal cirri are absent or rudimentary in 

 Scyliorhmus, but he separates Poroderma, an 

 Indian Ocean genus, from Scyliorkinus in his 

 key by the complete absence in Poroderma of a 

 rudimentary nasal cirrus. This rudimentary cir- 

 rus, in the material I have examined, is merely 

 a thickening of a portion of the anterior nasal 

 flap, broader and thicker near the base of the flap, 

 narrower and thinner near the posterior margin 

 of the flap, but not extending at all beyond the 

 edge of the flap. If one is familiar with the shape 

 of nasal cirri of orectolobid sharks, this structure 

 looks like a nasal cirrus entirely embedded in the 

 flap. I find it difficult to accept the idea that this 

 is necessarily a rudimentary structure and suspect 

 that it may function in directing the flow of water 

 past the nasal aperture. 



Nevertheless, differences in skin structures near 

 the mouth and nasal apertures may be of great 

 usefulness in the practical description of species 

 and as criteria for their identification, especially 

 among Indo-Pacific forms. 



REVIEW OF WESTERN ATLANTIC CAT SHARKS 



619 



