490 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



species, both inhabitants of moderate depths, it is remark- 

 able that its larva should occur in such large numbers in 

 the comparatively shallow waters of a bay like that of 

 Port Erin, where the tidal current of the open sea is but 

 slightly felt; and that the larva of Spatangus purpureus, 

 a much larger species, should not have been similarly 

 distributed in its own season. 



The only Spatangoid larva which remains to 

 be mentioned is that of E chinocyamus pusillus, for 

 an account of the development of which we are indebted 

 to Theel (15). The echinopluteus of this species 

 (fig. 65, PL IX) is stoutly built, and has arms of 

 moderate length. It is easily recognised by the uniform 

 fenestration of the skeletal rods of the post-oral and 

 postero-dorsal pairs of arms, and by the somewhat com- 

 plicated disposition of the body skeleton. Here again in 

 E chinocyamus pusillus we have an inhabitant of moderate 

 depths which, on account of its small size and dull green 

 colour may be overlooked in the contents of the dredge; 

 but which, judging from the number of its dead and 

 denuded tests in a bottom deposit which occurs within a 

 short distance of the Calf of Man, is probably not uncom- 

 mon in the neighbourhood of Port Erin. Its larva, how- 

 ever, has rarely occurred in the plankton. A small 

 number of fully developed echinoplutei were collected by 

 Gravely and myself by means of a weighted tow-net in 

 July and early August, 1907, and I have since seen an 

 occasional specimen in surface tow-nettings on various 

 dates during the autumnal months, the last being 

 November 1st, 1913. 



Larvae of Holothuroidea. 



The occurrence of larvae of Holothuroidea in the 

 plankton of Port Erin Bay has been of remarkable rarity 



