W. G. STEVENSON. 89 



lunate and a caudal peduncle carinated, gill-openings of 

 moderate size, and well-developed teeth, are the charac- 

 teristics which place this shark in the family Lamnidoe 

 (the porbeagles), which is thus described : l ' Large size, 

 with body stout, the mouth wide, with large teeth, and 

 the caudal fin lunate, the two lobes being not very 

 unequal, the upper lobes strongly bent upward ; caudal 

 peduncle with a keel on each side ; gill-openings wide, 

 all in front of the pectorals, entirely lateral, not ex- 

 tending under the throat ; first dorsal large ; pectorals 

 large ; ventrals moderate ; second dorsal and anal very 

 small ; pit at the root of the caudal ; spiracles minute or 

 absent ; genera, three ; species, six or more. Those in- 

 habiting our coasts have been much confused by 

 authors." 



The specimen which is the subject of this study differs 

 from this family description (1) in the position of the 

 last branchia3, which partly overlap the pectorals, and 

 (2) in the absence of a pit at the root of the caudal. 



This family — Lamnidoe — includes three genera, viz : — 



i Isurus ; 

 < Lamia; 

 [ Carcharodon. 

 These are distinguished from each other by the form and 

 construction of their teeth. 



The genus Isurus has two species, (1) /. dekayi (J. 

 & Gr.) — mackerel shark. [Syn. — Lamna punctata (De 

 Kay), Isuropsis de kayi (Gill), Lamna glauca (Gun- 

 ther) — ]. (2) /. spallanzanii (Raf.) [Syn. — Lamna 

 punctata (Storer) — ]. Jordan and Gilbert say there is no 

 evidence that this last named species is found in our 

 waters. 



Both species of the genus Isurus have teeth, "long, 

 lanceolate, with sharp, entire cutting edges and no basal 

 cusps," which excludes the specimen before us from this 

 genus ; it is also excluded from the genus Lamia, because 



41 



