Dr. J. E. Gray on the genus Assiminia. 423 



the tentaciila. jNIantle open behind. Fseces elhptical (as in Cydo- 

 stomd). Operculum corneous, ovate, spirally striated. The most 

 remarkable circumstance in this animal is the position of the eyes, 

 at the tips of the tentacula, as in Helix and its allies, and not at 

 the base. It would apjjcar as if there were in reality no tentacida, 

 and only the tubercle common to many Mollusca at the base of the 

 tentacula a little more developed than usual. The shell is so like 

 that of some species of Rissoa, that it is quite surprising that in 

 Dr. Fleming's ' British Animals,' and in Mr. Jeifreys' paper in the 

 * Linnsean Transactions,' it should be placed in, or close to, the 

 genus Limncea. Dr. Leach seems to have formed his conclusions from 

 an actual inspection of the animal, and consequentlj' made a distinct 

 genus for its reception. In many points the animal resembles very 

 much that of Cyclostoma, and is perhaps a step nearer than that and 

 Helicina, which have the mantle open behind, to the Pectinifo'a. 

 Its nearest ally, however, amongst the pectiniferous Mollusca I 

 should conceive not to be Rissoa. 



The animal and shell are figured in Forbes and Hanley's 'British 

 Mollusca,' iii. 70, t. 71. f. 3, 4, and t. H.H. f. 6. 



" Mr. Benson, at page 463 of the same volume of the Zool. Journ., 

 has given the foUowiug description of the animal of Assiminia fas- 

 ciata {Turbo Francesii, Gray, in Wood's Supplement, t. C. f. 28) : 

 — " Animal : Head with only two short, thick, subcylindrical ten- 

 tacula, \\ith the percipient points placed at their summits. Snout, 

 like that of Paludina, transversely corrugated and bilobed, or rather 

 emarginate at the centre of the extremity, the lobes rounded. Mantle 

 free, and branchial cavity open. Foot with a spiral homy operculum, 

 angular at the upper part." 



I may add to these descriptions that Mr. Clark has lately stated that 

 the tentacula of Truncatella Montayui are "short, flat, broad, triangu- 

 lar, and diverge greatly, scarcely forming an angle of 25°. The eyes 

 are large and black, and have white prominent pupils, which visibly 

 dilate and contract. I have never observed such in any mollusk, 

 though similar ones may have escaped notice ; they are placed a 

 little nearer to the base than the middle of their lower half, not on 

 pedicles, but quite flat on the centre of semicircular expansions of 

 the outer side of the tentacles, with an external tendency. The 

 branchial plume is single, of an elongated, kidney-shaped figure, and 

 has the usual constriction or sinus at the end nearest to the heart ; it 

 can be detected with high powers in sunlight, through the body 

 volution of pale, clear, thin shells." 



The eyes of Truncatella littorea " are precisely those of T. Mon- 

 tagui, and a similar white pupil is a singular coincidence." 



In conclusion, I may observe, that I regard the general form and 

 organization of the animal and shell of Truncatella as so peculiar, that 

 I iiave long considered it the type of a peculiar family, characterized 

 by the form of the lips and feet, the mode of walking, the short, 

 broad, diverging tentacles, the position of the eye and its peculiar 

 form, and the truncation of the shell. 



