2*76 W, BLAXLAND BENHAM. 



Along the upper base of the caudal are also a few shorter 

 and less distinct rod-like structures, but I do not feel sure 

 that in this case they are not the transverse walls of empty 

 fin-ray boxes ; the animal was lying in an awkward position, 

 and though there was a gap between the dorsal rod-like 

 structures and the hindermost distinct fin-ray boxes, yet the 

 higher surface of the body was here slightly injured and 

 torn, so that it was not possible to trace the continuity of the 

 two series. 



At first I imagined that we had in this species an interest- 

 ing vestige of the peculiar caudal fin rays of the early larva, 

 as figured in Lankester and Willey's memoir^ (pi. xxix, 

 fig. 1). But on examining the tail of a specimen of H. 

 bassanum I found that it was unnecessary to explain the 

 appearance in this temptingly interesting manner; for in 

 H. bassanum I find that the fin rays of the ventral fin 

 are continued past the anus along the under surface of the 

 body to the antepenultimate myotome (fig. 6) : it is true they 

 and their " boxes " are smaller here than in the true ventral 

 fin, anterior to the anus, but they are perfectly distinct right 

 along the base of the caudal fin. 



These ventral rays extend further backwards than do the 

 dorsal fin rays, which are here only represented by a series 

 of empty boxes and irregular "lymph-spaces;" in fact, the 

 ''rods" in H. hectori are the shallow transverse walls of 

 the empty fin-i'ay boxes. This post-anal extension of the 

 fin rays does not appear to have been noted " in any other 

 member of the group; and in A. lanceolatus Lankester 

 states definitely that they cease in front of the anus, and I 

 have examined mounted specimens myself and can confirm 

 this statement. 



In connection with H. bassanum I have to correct 

 what appears to be an error in Kirkaldy's diagnosis of this 

 species, where it is stated (p. 314) that the ventral fin-ray 



^ Lankester and Willey, "Development of the Atria! Chamber in Aniplii- 

 oxus," 'Quart. Journ. Micr. Sci.,' xxxi. 



2 "Contributions fo the Knowledge of A. lanceolatus," 'Quart. Journ. 

 Micr. Sci.,' xxix, p. 373. 



