360 



turn, I need only quote the learned authors of the ' British 

 Mollusca/ who, speaking of the Rissoa striatula, remark, 

 ' ' The animal of this, as of too many other Rissoce, is yet 

 unknown." 



I have reviewed, at Exmouth, the several species already 

 alluded to, and added some new ones ; I may therefore speak 

 with increased confidence of their descriptive accuracy as far 

 as regards the external organs, but I apprehend that a correct 

 anatomy of such minute creatures is a vain expectation ; we 

 must therefore rely on analogy, for at least the general 

 characters of their interior organization. 



It is necessary to mention that the almost microscopic 

 organs of these diminutive species require the aid of good 

 glasses to see their true forms and attributes; the present 

 descriptions are the result of the organs being viewed through 

 Coddington lenses of as high powers as were consistent with 

 distinctness: inferior means give false appearances, and are 

 often the cause of discrepancies between observers of the same 

 animal. 



R. STRIATA, Montagu. 



JR. striata, Brit. Moll. iii. p. 94, pi. 78. f. 8, 9. 



Animal inhabiting a white shell of 5-6 rather tumid, semi- 

 plicated, spirally striated volutions ; it is hyaline-white in most 

 parts; an exception is the upper and under surface of the 

 rostrum and buccal fissure, which are of a sordid light red- 

 brown. Mantle even with the shell, except that a minute 

 cirrhal filament, very difficult to be seen, issues from it at the 

 upper angle of the aperture, as in the type R. parva, in which 

 it is never absent. 



The head is a long flat muzzle, deeply grooved above and 

 below, with minute lappets on the upper surface near its 

 termination, and on the march is carried a little in advance 

 of the foot. The tentacula are moderately long, divergent, 

 strong, but flattened, very little setose ; they do not attenuate 

 to points like the type, but are of the same breadth throughout, 

 and of opake snow-white; in progression they are extended 

 considerably beyond the head. The eyes are conspicuously 

 black, and placed on minute, scarcely projecting, external 



