Mr. A. Adams on new Molluscafrom Japan. 477 



In some unequally grown Dactylopone we can trace the co- 

 existence of the more compound with the simpler form of struc- 

 ture. Thus in some tapering specimens we can discern in. the 

 thicker part that the large caBcal cells have been developed, 

 which are characteristic of D. cylindracea, whilst the caeca gra- 

 dually diminish and disappear in the constricted portion, which 

 approaches in its structure to that of D. Bambusa. 



All these peculiar organisms, recent and fossil, are related 

 within specific limits, the passage from the simple to the com- 

 pound being step by step, and not unlike similar transitions and 

 gradual complications seen in Orbitolites and others of the 

 ' ' opake " Foraminifera. According to our plan of choosing for 

 the type of a species the form furthest removed from extremes, 

 and yet indicating the main essentials of the structural features 

 of the whole specific group, we select D. Bambusa for the typical 

 form. 



The structural details of Dactylopora deserve full attention : 

 the brief descriptions given above are but indications of its 

 peculiar construction. 



Besides the French and Belgian Eocene Tertiaries, the Mio- 

 cene beds of San Domingo yield Dactylopora. 



[To be continued.] 



LI. Mollusca Japonica : New Species of Chrysallida and Par- 

 thenia. By ARTHUR ADAMS, F.L.S., &c. 



THE Sea of Japan appears to be as well stocked with the smaller 

 species of Pyramidellidce as the seas of Europe. The reason 

 why Clark speaks of this family as a " truly British group, which 

 far outnumbers the discoveries of any other country," is that 

 these little Mollusks live in comparatively deep water, and no 

 naturalist has hitherto brought them to light. By some hard 

 work and perseverance I have discovered many new Mollusca in 

 different parts of the world, and I shall now describe eight spe- 

 cies of Chrysallida and three of Parthenia from Japanese waters. 

 In another communication I shall give descriptions of some new 

 species of the allied genera, such as Turbonilla, Odostomia, Dun- 

 keria, Aclis, and Ebala. Some of these forms may be found 

 also in the China Sea, as I frequently meet with examples of 

 species which are common to the south and the north of the 

 Korea Strait. 



N.B. In a former paper I gave the name Huxleyia to a new 

 genus of bivalve Mollusca. Should, however, this name have 



