34 On the generic characters 



tuation of the fins, and the shape of the teeth ; only in the genus 

 Rata this last character is uncertain, the teeth changing here 

 with the age and sex, so as to be a character which cannot be 

 depended upon, even in the distinction of species. The same 

 may be said, to a certain extent, of the scales of the skin, and 

 the shape of the snout. Fortunately, in a collection of Sicilian 

 fishes, presented by Dr. Schultz to our anatomical museum, 

 and in the admirable manner in which they are arranged, we 

 possess the means of comparing a great number of individu- 

 als of the same species, whereby we are enabled to determine 

 the limits of individual differences. 



The most important character by which the great order of 

 Skates, {Rata) differs from that of the Sharks, [Squall), is the 

 existence of a peculiar cartilage arising from the nasal part of 

 the skull, and extending toward, or even meeting, the anterior 

 part of the crest of the pectoral fin. This cartilage is found 

 in all the Skates, and also in Rhinobatus and Pristis ; where- 

 as there is no trace of it in any Shark. 



At the head of the order of Sharks we place the family of 

 the Scyllia, of which the following characters may be given. 



Fam. SCYLLIUM. 



An anal and two dorsal fins ; the first dorsal placed behind or opposite, but 

 never before the abdominal fins. The spiracles are distinct in all, and pretty 

 large in most of them. The eye-lid, (membrana nictitans) is wanting. 



The distinction of Cuvier, which is taken from the. distance 

 between the mouth and nostrils, is not sufficient, as it is a diffe- 

 rence only of degree. We confine the name Scyllium to such 

 Sharks of this family as have the anal fin placed nearer to the 

 head than the second dorsal fin. (11 species.) 



Gen. Pristiurus, Bonap. 

 Differs from Scyllium only by its long snout, and by a series of larger 

 scales, arranged like a saw, on the upper edge of the tail. (1 sp.) 



Chiloscy Ilium, Nobis. 

 Anal fin placed farther back than the second dorsal, and the last bran- 

 chial opening approximating to the fourth. The characteristic mark of this 

 genus is the broad, membranaceous under lip, separated from the skin of the 

 throat by a kind of furrow. The upper nasal valve bears a cirrhus. (4 sp.) 



Hemiscy Ilium, Nob. 

 Situation of the fins is as in the preceding genus ; the nose and mouth as 

 in Scyllium. (1 sp.) 



Crossorhinus, Nob. 

 Remarkable for a great number of small membranaceous lobules, situa- 

 ted between the nostrils, and the first branchial opening. The mouth is 

 nearly at the top of the head. The two dorsal fins are placed towards the 

 posterior end of the animal ; the first of them being situated above, and a 

 little behind, the abdominal fins. (1 sp. the Squalus lobatus, Bl. Schn.) 



