18 Messrs. H. & A. Adams on new Genera of Mollusca, 



IV. — Descriptions of Five New Genera of Mollusca. 

 By Henry and Arthur Adams. 



Many interesting forms of Mollusca have been made known 

 since the publication of their ' Genera ' by the authors; and 

 many, doubtless, yet remain undiscovered. Several entirely new 

 types from Japan have recently been described in the ' Annals ' 

 by one of the authors ; and in this communication will be found 

 notices of five others, which are also supposed to be forms new 

 to science. Some of these, unfortunately, are from localities at 

 present unknown to us. 



Genus Leuconyx, H. & A. Adams. 



Testa interna? unguiformis, spathulacea, alba, extus convexa, intus 

 concava, impressione musculari nulla, marginibus inflexis, apice invo- 

 luto, uncinato, producto, cryptiformi. 



This genus is founded on a remarkable shell in the possession 

 of R. Tyler, Esq., and appears at first sight to belong to Capu- 

 lidse. The interior, however, is not marked by any horse-shoe 

 muscular impression. After repeated examination and compa- 

 rison, we have arrived at the conclusion that its real affinities 

 are with Aplysiidse, and especially with the genus Dolabella, 

 from which it differs principally in the contorted unguiculate 

 apex, which forms a cryptiform cavity somewhat similar to that 

 of Navicella and Crypta ( Crepidula of Lamarck) . On account 

 of its colour, form, and texture, we may consider it to have been 

 an internal shell, and covered by the mantle of the animal. 



Leuconyx Tyleriana, H. & A. Adams. 



L. testa spathuliformi, antice dilatata, postice unguiculata, alba, 

 tenui, superficie longitudinaliter substriata lineisque concentricis 

 incrementi insculpta ; margine dextro concavo, breviore, sinistro 

 rectiusculo, longiore ; apice intorto, intus concamerato. 



Hub. ? 



Genus Bacula, H. & A. Adams. 



Testa subulata, claviformis, imperforata, tortuosa, solida, tota trans-' 

 versim striata. Apertura ovata, antice Integra, producta ; labio in- 

 crassato, calloso ; labro simplici, margine acuto, in medio producto. 



In its subulate form and tortuosity this little genus resembles 

 Eulima, all the species of which, however, are glabrous or po- 

 lished. In Bacula the whorls are transversely striated, and the 

 inner lip is circumscribed and callous. 



Bacula striolata, H. & A. Adams. 



B. testa subulato-claviformi, imperforata, sordide alba, tota transver- 

 sim striata ; anfraclibus circa duodecim, planatis, ultimo ad peri- 



