Mr. A. Adams on new Mollusca from Japan. 41 



could perceive a reason for this difference, in the fact that the 

 Dorids and Polj^cerina? having special and effective branchiae, the 

 presence of spicula thickly distributed through the dermal cover- 

 ing would not so much interfere with their respiration as they 

 would with that of the Eolididae were their skin largely occupied 

 by them ; for these latter, having no special branchiae, require 

 an unimpeded surface for the vascular system to be brought as 

 much as possible in contact with the surrounding element. But 

 the fact that spicula are found even in the branchial plumes of 

 the Dorids and Polycerinae militates against this theory. On 

 the other hand, if what I have previously said is true, as to the 

 incorrect position hitherto assigned to the Eolidida3, we should 

 not be bound to expect that their external similarity of form to 

 the true Nudibranchiata should necessarily be accompanied by 

 an identity of internal economy. 



But, to return to the necessity whicb exists for an acquaintance 

 with immature forms, particularly among those who give names 

 to apparently new species, the history of the Nudibranchiata is 

 not without instances of the unnecessary multiplication of syno- 

 nyms arising from this fertile source. Messrs. Alder and Han- 

 cock tell us that Goniodoris nodosa has received several distinct 

 names from those who have observed it in different stages of 

 growth. When young, and before the tubercles have begun to 

 appear, they are the Goniodoris emarginata of Forbes; after a 

 time they assume the appearance of the Doris nodosa of ]\Ion- 

 tagu; and even when full-grown, the distention of the body 

 with spawn, by rendering the tubercles obsolete, has given rise 

 to the spurious Doris Barvicensis of Johnston. Other instances 

 of this kind might be cited ; but it must not be forgotten that 

 there is also a danger of falling into the opposite error — that, 

 namely, of mistaking a really distinct animal for the immature 

 form of another species. Thus, Tritonia alba was long regarded 

 as the young of 2\ Hombergii, ^^ntil distinguished by Alder and 

 Hancock; and Tritonia plebeia was also for some time imagined 

 to be the young of the same animal, until recognized as a distinct 

 species by Dr. Johnston. In all similar cases, the persistence of 

 characters in the smaller animals, added to a careful examination 

 of the tongue, will seldom fail to lead to a correct conclusion in 

 the end. 



VIII. — On some additional neiv Species of Pyraraidellidfe from 

 the Islands of Japan. By Arthur Adams, F.L.S. &c. 



Still pursuing my investigations among the members of this 

 little-known family of Mollusca, I have become acquainted with 



