224 CRETACEOUS PELECTPODA 



between the Soljenid^ and the TULLINAGBA and from these again to the 

 VUNEBACIjA, I should have certainly classed the present order immediately 

 after the MYA CJEA ; but considering our present materials, I prefer to look upon 

 the former named three orders rather as belonging to one series of shells, and provi- 

 sionally to separate the CSAMACUA from them. However, it cannot be doubted, 

 I think, that the relations pointed out are to a great extent correct, and when parti- 

 cularly the very numerous fossil MYA CUA and also the CSAMA CJEA have been 

 better studied, the classification of the one next to the other will most likely be 

 found the most natural one. 



Pictet and Campiche, in their recent classification of the cretaceous Pelecy- 

 poda of Sainte- Croix (Pal. Suisse, 5^^ ser., 4^' partie, 1868), propose a distinct order 

 for the GSAMACEA under the name of " Pleuroconques JDimy aires'' as equivalent 

 to their two other orders, '' Acephales orthoconques'' and ''A, monomyaires'' I con- 

 fess, I do not see either in the organization of the animals or shells anything to 

 support this grand division. 



All the recent CSAMA CJEA are littoral, living attached to rocks, or on coral- 

 reefs; the fossil HippuRiTiDJE often formed extensive banks similar to those of 

 oysters ; they belong with few exceptions to the fauna of tropical seas, and are all 

 purely marine inhabitants. The total number of known recent species is about 75 ; 

 in the tertiary period it is considerably smaller, but in the cretaceous period it is 

 more than double, very rapidly decreasing again in the Jurassic period. 



XYIII. Family— VFB TICOBDIID^. 



Shells equivalve, or nearly so, of small size,, inflated, with the beaks incurved, 

 closed all round, more or less solid, pearly inside ; hinge with few cardinal teeth 

 more or less obsolete, ligament sub-internal or internal ; two muscular impressions, 

 pallial line simple. The three genera which I propose to include in the present 

 family under the above mentioned characteristic are Fecchiolia, Verticordia, and 

 Allopagus, the last being proposed for the species Mippagus Leanus of Deshayes, 

 as it does not belong to Lea's genus, which I shall point out further on. 



Of these three genera we have only lately* become acquainted with the 

 animal of Verticordia^ the other two genera being as yet known only in the fossil 

 state. 



The animal of V. Japonica, A. Ad., has the mantle margins united, with a 

 small anterior opening for the protrusion of the foot, which is small, triangular, 

 compressed, and a posterior roundish, fringed opening in which are enclosed two 

 separated but very short siphons ; labial palps small. 



Mr. Adams justly observes that Verticordia has no relation to Trigonia with 

 regard to the organisation of the animal, and that it is more closely allied to 

 Glossus f=IsoGardiaJ, Considering the form of the siphons in Verticordia and the 

 general character in the form of the shell, this classification would certainly appear 



* Ann. Mag. Nat. Hist., 1862, vol. ix, p. 224. 



