Fishes of the Western North Atlantic 263 



rostral cartilages 3, united anteriorly^ radials of pectoral mostly on metapterygium; 

 meso- and propterygia much smaller} meso- and metapterygia separated by a foramen, at 

 least in some cases; heart valves in 3 rows. Development either ovoviviparous, or vivipa- 

 rous with well developed yolk-sac placenta. 



Genera. This is not only the largest family of sharks, but the majority of modern 

 sharks fall within it. All its western Atlantic members are inhabitants of the tropical or 

 warm temperate belts, only entering the boreal zone in summer with the vernal expan- 

 sion of high water temperatures, if at all. Some of them are cosmopolitan in the appropriate 

 thermal belt, but others are confined to comparatively narrow areas of distribution. The 

 majority of species are harmless, but a few bear evil reputations as dangerous to bathers. 



Key to Genera 



la. Anal nearly 4 times as long at base as 2nd dorsal. PAyjoiow Miiller and Henle, 1841. 



India, China, Australia. 

 lb. Anal at base less than 3 times as long as 2nd dorsal. 

 2a. Spiracles present, from large to minute. 



3a. Second dorsal originates behind rear end of base of anal. 



Loxoiow Muller and Henle, 1841. 

 Red Sea, Mauritius. 

 3b. Second dorsal originates over or in front of midpoint of base of anal. 



4a. Midpoint of base of ist dorsal considerably nearer to origin of pelvics 

 than to axil of pectoral. Thalassorhmus Miiller and Henle, 1 841 .' 



Eastern North Atlantic, Mediterranean. 

 4b. Midpoint of base of ist dorsal at least as near to axil of pectoral as to 

 origin of pelvics, or nearer. 



5a. Caudal peduncle with a low longitudinal dermal ridge on each sidej 

 upper labial furrow as long as snout in front of mouth. 



Galeocerdo Miiller and Henle, 1837, p. 265. 



5b. Caudal peduncle without longitudinal dermal ridges; upper labial 



furrow not more than ^^ as long as snout in front of mouth. 



6a. Inner margins of upper teeth regularly serrate nearly to tips, 



but without basal denticles; their bases very deeply incised in 



the midline. HemiprisUs L. Agassiz, 1 843. 



Red Sea.= 



1. The genus seems not to have been reported since i 88 i, when Moreau (Hist. Nat. Poiss. France, / .- 319) described a 

 specimen from Cette on the French coast of the Mediterranean. Watch should be kept for it, for it is likely to be 

 confused with Prionace, from which it differs chiefly in having- spiracles. 



2. We follow several previous authors in referring the Dhr/iizodon elongatus of Klutzinger (Verh. zool.-bot. Ges. 

 Wien, 11, 1871 : 664) to Hemipristis on the strength of Probst's (Wurt. Jahresh., 5.;, 1878: 141) statement that 

 the teeth of the single known specimen resemble very closely the fossil shark's teeth that have been described under 

 that name from the Upper Cretaceous to Miocene of North America, Upper Cretaceous to Pliocene of Europe, 

 Eocene and Miocene of Africa, Miocene of Asia and South America, and Tertiary of the West Indies. 



