20 



5. On THE Genus Assiminia (Leach). 

 By Dr. j. e. Gray, F.R.S., P.B.S. etc. 



In a list of some species of British shells at the end of an arrange- 

 raent of MoUusca in the 'LondonMedicalRepository' for 1821 (vol.xv. 

 p. 239), I noticed a new mollusk under the name of "Nerita {Syncerd) 

 hepatica, n. s. The animal of this shell differs from all others of this 

 order by the eyes appearing to be at the end of the tentacula, but I 

 believe that they are placed on a peduncle as long as the tentacula, 

 and the peduncle and tentacula are soldered together." 



Dr. Leach, when he examined the animal of this shell, formed it 

 into a genus under the name of Assiminia, and named the species 

 after myself as A. Gray ana, described under this name at the end of 

 the genus Limnea, in Fleming' s ' British Animals,' p. 275 (1828), 

 who observes, " Dr. Leach sent me several years ago a shell from 

 Greenwich marshes, constituting a new freshwater genus, under the 

 title Assiminia Grayana. The lip is thickened on the pillar and re- 

 flected over the cavity, but is destitute of the obliąue fold, and the 

 lip does not extend over the body whorl. The colour is brown ; 

 whorls six in number, conical, regularly increasing in size, glossy, 

 with minute lines of growth. Length about -i^ths of an inch." 



In my paper "On the Difficulty of distinguishing certain genera of 

 Testaceous MoUusca by their Shells alone, and on the Anomalies in 

 regard to Habitation observed in certain species," published in the 

 ' Philosophical Transactions ' for 1835, p. 301, I observe : "About 

 fifteen years since I first observed in the marshes near the bank of 

 the Thames, between Greenwich and Woolwich, in conipany with 

 species of Valvata, Bithynia and Pisidium, a small univalve shell, 

 agreeing with the smaller species of the littoral genus Littorina in 

 every character both of shell and operculum. Yet this very pecu- 

 liar and, apparently, local species has an animal which at once distin- 

 guishes it from the animal of that genus and from all Ctenobranchous 

 MoUusca. Its tentacula are very short and thick, and have the eyes 

 placed at their tips, while the LittorincB, and all the other animals 

 of the order to which they belong, have their eyes placed on small 

 tubercles on the outer side of the base of the tentacles, which are 

 generally more or less elongated. The shell in question and its 

 animal were described and figured by Dr. Leach in bis hitherto un- 

 published work on British MoUusca, under the name of Assiminia 

 Grayana, and as this name has been referred to by Mr. Jeffreys and 

 other conchologists, it may be regarded as established, and that of 

 Syncera hepatica, proposed by myself in the ' Medical Repository,' 

 vol. X. p. 239, will take rank as a synonym. A second species of 

 this genus has lately been made known by Mr. Benson, by whom it 

 was found on the ponds in Ihdia. Its shell is banded likę that of 

 Littorina A-fasciata and several other sm9\\a Littorince, and has 

 been figured in the Supplement to ' Wood's Conchology,' t. 6. f. 28, 

 under the name of Turbo FrancesieB." 



In my edition of 'Turton's Manual,' 1840, p. 88, I characterize 

 the genus thus : — Assiminia : Shell ovate, conical, solid ; mouth 



