96 Memoir Sears Foundation for Marine Research 



vertebral centra with calcareous lamellae radiating from a central ring, or with latter alone 

 calcified (genera Galeus, Pseudotriakis) ; neural spines not attached to dorsals; skull with 

 antorbital processes more or less developed, but no separate antorbital bar; rostral carti- 

 lages 3 (united or separate at tip), i or none; upper jaw (palatoquadrate cartilage) not 

 articulated with cranium, but connected with ethmoid region by a longer or shorter liga- 

 ment;' its connection with hyomandibular arch also ligamentary only, at least in most 

 cases/ Propterygial cartilage of pectoral much smaller than mesopterygium, with I to 

 several radial elements; heart valves in 2 or 3 rows; claspers of male projecting freely 

 from pelvics; axial cartilages either single or double, usually with a group of movable 

 accessory cartilages at the tip when adult, and attached to basipterygium of fin by i small 

 connecting element only." Development oviparous, ovoviviparous, or viviparous. 



Key to Families 

 la. Only i dorsal fin. Scyliorhinidae (part), p. 195. 



lb. 2 dorsal fins. 



2a. At least V2 of base of ist dorsal posterior to origin of pelvics. 



3a. Caudal lunate, large; gill arches connected one with the next by masses of 

 spongy tissue, forming sieve-like structures. Rhincodontidae, p. 187. 



3b. Caudal not lunate, not very large; gill arches not connected one with the next 

 by masses of spongy tissue. 



4a. Nostril connected with mouth by a deep groove, its anterior margin with 

 a well developed barbel. Orectolobidae, p. 178. 



4b. Nostril not connected with mouth by a deep groove, or, if so connected, 

 its anterior margin without a well developed barbel. 



Scyliorhinidae, p. 195. 

 2b. Base of ist dorsal terminates over, or (usually) well anterior to, origin of pelvics. 

 5a. Head greatly expanded laterally. Sphyrnidae, p. 407. 



5b. Head of normal shape, not expanded laterally. 

 6a. Caudal fin lunate, its axis steeply raised. 



7a. Teeth large, few in number; gill arches without gill rakers. 



Isuridae, p. 109. 

 7b. Teeth minute, very numerous; gill arches with well developed 

 rakers. Cetorhinidae, p. 146. 



6b. Caudal fin not lunate, its axis raised only moderately at most. 



8a. 1st dorsal fin longer at base than caudal. Pseudotriakidae, p. 228. 

 8b. ist dorsal fin much shorter at base than caudal. 



9a. Caudal fin occupies nearly J/2 total length, or even more. 



Alopiidae, p. 160. 



7. This allows the jaws to be more or less protrusible in many cases. 



8. Parker's (Trans, zool. Soc. Lond., lo, 1879: pi. 38, fig. 2) illustration of the skull of Scylliutn canicula, equals 

 Scyliorhinus caniculus (Linnaeus), 1758, which shows these ligamentary connections well, has been copied in many 

 subsequent textbooks of zoology. 



9. For illustrations of the cartilages of the clasper in various galeoids, see especially Huber (Z. Wiss. Zool., 70, 

 1901 : pi. 27) i White (Bull. Amer. Mus. nat. Hist, 74, 1937: pi. 46-50). 



