55 PROCEEDINGS OF THE ACADEMY OF [April, 



Mustelus mustelus (Linnaeus). 



(M. equestris Bonaparte, Icon. Faun. Ital., Pesc. Ill, pt. 2, vii, 1834, descr., 

 PI., fig. 2, mari d'ltalia.) 



Head 6^; depth about 9; width of head 1| in its length; depth of 

 head at posterior margin of eye 2^; snout measured to eye 2f ; eye Sf; 

 width of mouth 2f ; interorbital space 2f ; width of internasal space 

 6|; front margin of first dorsal 1^; of second dorsal 1|; of anal 2|-; 

 least depth of caudal peduncle 6f ; front margin of lower caudal lobe 

 2to i upper margin of pectoral lj\ ; front margin of ventral 2. 



Body very elongate, depressed in front, sides well compressed, and 

 tapering posteriorly into a long slender caudal, greatest depth about 

 origin of first dorsal. Edges of body rather slightly convex or de- 

 pressed, a very obsolete or shght median ridge down back most pro- 

 nounced on upper surface of caudal peduncle, and down postventral 

 and postanal regions a well-developed deep median groove. Caudal 

 peduncle slender, compressed, and its least depth about If in its 

 length. 



Head well depressed, profiles tapering similarly, and as viewed above 

 rather elongate wdth somewhat attenuately convergent margins though 

 tip rounded. Snout broadly depressed, edge rather trenchant, and 

 its length but a trifle less than its width. Eye elongate, large, laterally 

 superior, and placed about midway in length of head. Mouth rather 

 broad, symphysis of mandible slightly in front of anterior margin of 

 eye, and rami would nearly form a right angle. Lips thin and hardly 

 developed. At angle of mouth externally a rather long fleshy fold 

 forming a well-developed flap projecting posteriorly, and though 

 groove distinct posteriorly around it, it extends but very little along 

 outer margin anteriorly. About 55 series of blunt tubercles or pave- 

 ment-like teeth in each jaw. Buccal folds rather narrow. Tongue 

 large, broad, its surface minutely asperous, and edges all free and sharp. 

 Nostrils large, well separated on each side of snout below, near last 

 third in length of latter measured to eye, and each with a well-developed 

 flap. Interorbital space broad, well depressed, and but very slightly 

 convex. 



Gill-openings 5, last 2 over base of pectoral, and third deepest or 

 about 2 in interorbital space. Spiracle small, distinct, and placed 

 behind eye a space equal to about ^ its horizontal diameter. 



Body covered everywhere with minute shagreen denticles of uniform 

 size. 



Origin of first dorsal much closer to origin of pectoral than that of 

 ventral or a little nearer tip of snout than origin of second dorsal, its 



