SQUALIDiE RAFINESQUe's GENERA. 129 



main entirely unknown to all naturalists who have 

 followed him. 



1. G. C ARCH ARIAS. No spiracles : dorsal fins two ; 

 anal one : five branchial apertures on each side : tail ob- 

 lique, unequal. — Obs. This genus is the first among the 

 Squalini, and contains those species which are the largest 

 and the most voracious. It is strikingly distinguished 

 from the genus Galeus, by the absence of spiracles. 



2. Dalatias. No spiracles : two dorsal fins, but 

 no anal ; five branchial apertures on each side : tail 

 unequal,, oblique. This genus differs from the last by 

 wanting the anal fin ; and from that of Squalus proper, 

 by the absence of spiracles. Teeth flat, long, acute, 

 disposed in a single row on the under jaw, and in two 

 on the upper, where, also, there are others much smaller: 

 eyes round : the branchial apertures are rather large. 

 Two species are described, — D. sparophagus and noc- 

 turnus. The latter has the anterior part of the dorsal 

 fin spined, and the posterior acuminated ; the head has 

 numerous pores : habits nocturnal: length seldom above 

 three feet : the teeth are unequal, acute, disposed in 

 various ways : dorsal spine united half way to the fin : 

 branchial apertures narrow. The pores on the head are 

 very remarkable : they are easily seen, although very 

 small ; and are round, unequal, and irregularly scattered 

 on each side of the head, from the tip of the snout to 

 above the eyes. 



3. Tetroras. No spiracles : two dorsal fins, and 

 one anal : branchial apertures rather large, four on 

 each side : tail unequal, oblique. 



4. IsuRus. No spiracles: dorsal fins two, the pos- 

 terior adipose; anal fin one, adipose: branchial apertures 

 five on each side : tail vertical, equally divided, and 

 lunulate. This genus is remarkably distinguished from 

 all others in this order, by the form of its tail, — a form 

 which is not seen in any other, and from which the 

 name is derived.* 



* The only species known to our author is described in the following 

 words, where he introduces those other characters which belong to the 



VOL I. K 



