St. Andrews Marine Laboratory. 107 



much expanded, has a perfectly sinootli edge, and the anal 

 cone is in the centre. 



The bristles have the usual microscopic structure, and the 

 anterior hooks differ from the posterior in the shape of tlie 

 crown and in the absence of the process under the great fang. 

 The bristles and hooks of the posterior segments, viz. from 

 the thirteenth to the twenty-third, are best developed. 



No tube accompanied the specimen, but in the Zt^tlandic 

 example the somewhat firm though friable tube is composed 

 of sand-grains and minute fragments of shells cemented to- 

 gether by secretion, and it apparently resembles that figured 

 by Audouin and Edwards. 



4. On the Atlanta-Wee Larval Mollusk. 



A few remarks were made under the Xth Series of " Notes 

 from the Marine Laboratory " * on a minute Atlanta-like form 

 which had been found in the tow-nets in St. Andrews ]5ay, 

 A single examj)le had been obtained, and it was only observed 

 after having been immersed in spirit for a considerable time. 

 In 1890 and in 1891, however, many specimens of the same 

 form appeared, and the shell was observed to be elastic (un- 

 calcified) and very minutely spinous, as shown in the 

 accompanying drawing kindly made from the living animal 

 by Mr. E. W. L. Holt (Plate VIII. fig. 5). The frequency of 

 the form in the tow-nets, together with its minute size, 

 showed that it probably was a larval stage of a mollusk not 

 uncommon in the neighbourhood. Its relationship with the 

 young Lamellaria, as described by Dr. A. Krohn, was indeed 

 soon afterwards kindly pointed out to Mr. Holt and myself 

 by Mr. M. F. Woodward. 



A larva allied to the foregoing was first procured by Dr. A. 

 Krohn at Messina, in March, and described as a new mollusk 

 under the name of Echinospira diaphana f. The shape of 

 this form, however, considerably diverges from that pro- 

 cured at St. Andrews, and the spines are much larger. Two 

 years later the same author pointed out that the foregoing 

 Echinos'pira diaphana was the larva of a pectinibranchiate 

 Gastropod, and he subsequently described another species also 

 obtained in the tow-net, in February, at Messina \. In the 

 latter paper a full description of the horny shell and the 

 structure of the larval mollusk are given ; while the relation- 

 ship of the form to the Marsenidai {Lamellaria &c.) is indi- 



* Ann. Nat. Hist., January 1890, p. 47. 



t Archiv f. Naturg-esch. 1853, p. 223, Taf. xi. figs, i., ii. 



X Ibid. 1857, p. 252, Taf. xi. ii},-s. 1-4. 



