NATURAL SCIENCES OF PHILADELPHIA. 497 



2. Teeth of upper jaw oblique, with the inner margin con- 

 tinuous from the base; those of lower jnw with the 

 points directed obliquely outwards, and with entire 

 inner incisoral edges. Scales rather large, cordate 



and keeled along middle Lepidorbinus. 



B. Teeth in upper or both jaws digitate or with a large acute 

 central cusp, and one or more smaller acute cusps 

 on each side, as in Scyllium. Scales hair-like or 

 quadrangular with an upright point. 



1. Teeth of upper jaw only digitated ; of lower like those of 



Squalus. Scales hair-like Spinax. 



2. Teeth of both jaws digitated. Scales quadrangular, 



each with an upright point Centroscyllium. 



Genus SQUALUS (Artedi,) Raf. 



Squalus Artedi, Linn. 



Squalus Rafinesque, Caraterri di alcuni nuovi generi e nuovi specie, &c, p. 

 12, isio. 



Acanthorhinus Blainville, Journal de Physique, &c, tome lxxxiii. p. 263, (type 



5. acanthias,) Oct., 1816. 

 Les Aiguillats (Spinax) Cuvier, Regne Animal, ed. 1, vol. ii. p. 129, 1817. 

 Acanthias Bonvparte, Selachorum Tabula Analytica. 



Body fusiform, slender, with the caudal peduncle also elongated and 

 slender. 



Scales cordiform or heart-shaped, with a middle point, and one or more keels 

 on each side. 



Head oblong-ovate and flattened, with the muzzle projecting and subconic, 

 but blunt at its extremity. 



Eyes above the mouth, longitudinal and with subcircular pupils, flop from 

 the nostril, nearer the snout than the mouth ; each with a produced border. 



Spiracles large behind and slightly above the eyes, crescentiform convex in 

 front and with a valve at its front margin. 



Mouth little arched in front. Labial cartilages two above and one below. 



Corner pits of the mouth large and obliquely point outwards and back- 

 wards. 



Teeth nearly similar in each jaw, subquadrate, with the incisive edge nearly 

 horizontal, and at the external angle terminating in a point directed outwards 

 and separated by a notch from the body. The root of each tooth is higher on 

 its inner side than its outer, and has on the former a longitudinal keel ; on the 

 outer forms a round ledge towards the point of the tooth. 



Dorsal fins moderate, with a nearly naked spine in the front margin, each fin 

 rounded at its anterior angle, and with the posterior acutely extended back- 

 wards. First dorsal larger, much nearer to the pectorals than the ventrals. 

 Second, far behind and with the spine proportionately larger. 



Caudal lin with the upper lobe much developed and the membrane increasing 

 in height towards the end above the caudal vertebrae, rounded at its end and 

 regularly incurved to the sinus separating it from the lower lobe which is mod- 

 erately developed. Tail pits developed at least at the base of the upper caudal 

 lobe. 



Pectoral fins produced at the external angle, which is rounded, and incurved 

 at nearly right angles to the inner angle, which is more or less blunt. 



Ventral fins submedian, little nearer to the second dorsal than the first, ob- 

 tusely angulated in front, and acutely angulated behind. 



The claspers of the male are furnished on the exterior side near the end with 

 a moveable prickle or spine whose tip is curved. 

 Type. Squalus acanthias Linn. 

 The present genus is here restricted more precisely than has been done, 



1862.] 35 



