628 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxvi. 



Order III. TECTOSPONDYLI. 



Calcareous liuiu'lhi' arranged in one or more concentric series or 

 rings about a central axis in each vertebra. Spiracles present. Anal 

 fin wanting. Dorsal fins 2, with or without spine. As here under- 

 stood, the order Tectospondyll includes the sharks of the groups called 

 Oyclospondyli and Tectosjwndyll by Hasse. The vertebr{\3 in the order 

 of Kays show similar structures, and it is probal)le that from sharks 

 of this group the Kays are descended. 



(TtKTc^i\ builder; ff7rov6i>\o5., verte})ra.) 



FAMILIES OF TECT08P0NDYLT. 



a. Cyclospondyli: Vertebnc with calcareous lamelLe arranged in a ring about the 

 central axis; pectoral fins normal, not expanded or deeply notched; anal lin 

 absent; spiracles present, no nictitating membrane; gill-openings before pec- 

 torals; caudal bent upward, lower lobe little developed. 

 h. Dorsal fins each provided with a stout spine, first dorsal far in advance of 



ventrals Suualid.e, XIII. 



bh. Dorsal fins without spine, first dorsal over or in advance of ventrals. 



r. Snout not produced in form of a saw; no l)arbels; first dorsal much l:»efore 



ventrals; skin moderately rough Dalatiid^, XIV. 



CO. Snout produced in a long, flat ))lade, with sharp, saw-like teeth on each side; 

 a pair of barl)els below snout; first dorsal i)efore ventrals. 



PRISTIOPHORIDiE, XV. 



act. TErTospoNDYLi: Vertebne with calcareous lamelhe ranged in several concentric 

 series or rings about a central axis; pectoral fins very large, expanded hori- 

 zontally, and extended forward at base in front, giving body the form of the 

 flattened disk of rays; anterior extension separated from neck by a deep ntitch, 

 in which gill-openmgs lie; no anal fin; dorsal fins small, posterior; mouth 

 broad, anterior Squatinid.e, XVI. 



Family XIII. SQITALID.F. 



'D()(4-FISHES. 



Body more or less elongate. Head depressed. Eyes lateral, without 

 nictitating membrane. Mouth inferior, rather large, arched, a deep 

 groove on each side. Teeth compressed, variously formed. Nostrils 

 inferior, separate; spiracles rather large; gill-openings moderate, all 

 in front of the pectoral tins. Dorsal tins 2. each armed with a spine; 

 the first dorsal in front of the ventrals; anul lin wanting; caudal fin 

 with the lower lobe small or ob.solete, ventral tins inserted posteriorly, 

 not much before second dorsal. Oviparous. Genera 6 or more; 

 species about 15; rather small sharks, chiefly of the Atlantic. These 

 sharks represent a comparatively primitive type, apparently not 

 descended from any oth(M' existing Sqadll. 



n. r.ddy rather elongate, no fold of skin along side of belly; dorsal spines hoth 

 directed hackwani. 



