274 W. BLAXLAND BENHAM. 



the genus Heteropleuron, for which I propose the name 

 H. hectori. 



The specimens had apparently been preserved in osmic 

 acid^ for they are dark grey ; and though they had received 

 various slight injuries to the side of the body and to the 

 fins, they are in sufficiently good condition to enable me to 

 make out all the important specific characters. One of the 

 specimens I was permitted to open, doing as little damage to 

 it as possible ; and afterwards I cleared it in oil of cloves for 

 more detailed examination of certain parts. 



The extreme tips at both ends of the body in each specimen 

 were more or less injured, but by comparing the two I have 

 been able to reconstruct, with some confidence, these ends. 

 The injury affects the tip of the caudal fin, and part of the 

 rostral, which was folded round the side : in the case of the 

 latter the outlines are in the drawings represented by 

 dotted lines, as there is some doubt as to the exact form of 

 the fin ; while the general curvature of the upper and lower 

 margins of the caudal tin, preceding the injury, suffices to 

 show that probably the fin is naturally of the form shown in 

 the drawing. 



Heteropleuron hectori, n. sp., has a length of about two 

 inches, the actual measurements being 48 mm. and 49 mm. 

 respectively. 



The myotomes number 84 or 85, and the myotome 

 formula is 53 + 19 (20) + 12, i. e. there are 53 myotomes 

 from the anterior end to the hinder margin of the atriopore, 

 19 or 20 thence to the posterior margin of the anus, and the 

 remaining 12 are post-anal. The last two or three are very 

 small, and the usual difficulties in deciding as to the exact 

 number of myotomes between atriopore and anus were en- 

 countered. But from careful examination of the two speci- 

 mens, I believe that the above formula (which, as Kirkaldy's 

 paper ^ shows, is subject to individual variation in all species) 

 is correct. 



The dorsal fin is very shallow over the greater part of its 



' " Revision of tlie Branchiostoniidic," 'Quart. Journ. Micr. Sci.,' xxxvii. 



