$ ">. CANCEI; IHKUF.^ VITKRUM. Plate XLV. figs. 10, 11, VJ. 



A- ue h.ive .ii-tm-ui-li.'.l tip- < Yu-t.i '.MII- l>y an m<lm.it.-'l nit.-_'u 

 in. -at. it mi^ht !> inferred the quality of the covering of the whole pre- 

 sents mu.-h similarity. This, however, would be erroneous, for beginning 

 with what i- :is hard as a nut shell, we should soon arrive at what may 

 be compared, in softness and tl.-xil'ility. to mechanical manufactn. 

 Some are tenacious without hrittleneas. 



But the only example occurring to me of great deviations from the 

 ordinary principle an- in two species; first, the female of the CH IK-IT 

 Horridus, on whi.-h we shall pass no further observation at present 

 secondly, the 1'inHntln-n-a ret, , inn, which merits a few special remarks. 



The history of this latter animal has embarrassed naturalists, nm 

 can I hope to contribute much to its elucidation, owing to the extreme 

 rarity of the species. 



It is one of the smaller animals inhabiting the Scotch seas, and it 

 seems to be most irregularly distributed in the British Islands. Dwelling 

 at all times apparently in society of another, the most unlikely of any 

 associate, the J////i/. ;W/W.v, their history is generally interwoven to- 

 gether. I think it is Dr Leach who says he found only three specimens 

 in the Mi/tilus mmliitlus, or horse mussel, whereof he o^-ned MO h-v than 

 one hundred specimens in que.-t of them. Mr W. Thompson, howe\ 

 and Mr T. V. Thomson were more successful on the coast of Ireland, as the 

 former observes, that, on opening eighteen mussels, he found fourteen of 

 the Pinnotheres, all females, and he quotes the latter, Mr T. V. Thomson 

 in remarking, that, by the dredge, on any bank of old Afodioli or I'intur, 

 where the Pinnotheres has been observed, almost every shell will be found 

 to contain one full grown female, some two, and others three, independent 

 of young ones, and males occupying them in common with the females. 

 W. Thornton, Ap. ; Annals and Magazine of Natural History, Vol. X. 

 p. 274. 



Although fine specimens of the AfylUus modiolut abound in various 

 parts of Scotland, I cannot discover that the frequency of the Pinno- 

 theres corresponds in any respect, or has been thus recovered. It does 



