224 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



has a long anal siphon and a long vermiform foot. As regards the 

 shell, I do not consider the surface sculpturing to be of much 

 importance, but the hinge-line is almost always crenulated behind the 

 ligament. From Dr. List's monograph, above quoted, we learn that 

 the arrangement of the muscles in Modiolaria is very different from 

 those of other genera. In M. marmorata the posterior adductor is 

 much smaller than the anterior ; the byssal retractors consist of three 

 separate muscles, viz., anterior and posterior retractors of small size 

 and a middle group of muscle-cords which are inserted high up, below 

 the ligament in an uninterrupted line. This division into a median 

 byssal retractor recalls that in Chloromya, but the scar is very different 

 in shape. 



Modiolaria therefore may well retain the generic rank which has been 

 given it. I think Fischer was right in placing Gregariella under it as 

 a subgenus. The shell originally described as Mudiola opifex is also 

 a Modiolaria ; for this shell Dr. Dall proposed the subj^enus Botidina, 

 but he has since admitted that this is a synonym of Gregariella, so 

 that opifex may be included with G. Petagn<z. 



Rhomhoidella. Monterosato, 1884, only differs from Modiolaria in 

 being striated all over, and cannot rank as more than a subgenus. 



Other recognised genera of Mytilidse are : — Idas, Jeffreys, 

 Dacrydium, Torell, and Crenella, Brown. 



In conclusion, I desire to tender my sincere thanks to all those who 

 have assisted me by imparting information or by the loan of specimens, 

 viz., to Messrs. R. H. Burne, J. E. Cooper, A. Hartley, Rev. A. H. 

 Cooke, Dr. W. E. Hoyle, Mr. J". C. Melvill, Mr, J. MacAndrew, and 

 Mr. E. A. Smith. 



