JOUSSEAUMIA. 245 



It is extremely difficult to get a clear view of the hinge teeth in very small hivalve 

 shells. Bernard (3) has remarked on the unsatisfactory results obtained from dry 

 specimens mounted on black paper and recommends fixing them direct on a glass 

 slide and varying the sub-stage illumination. I found that much the most satisfactory 

 results were obtained by thoroughly cleaning the shells in potash or Eau de Javelle 

 and then mounting them under a coverslip in glycerine jelly. By altering the 

 sub-stage illumination and rotating the stage one can get very clear pictures of the 

 minutest details. 



After a careful examination of the shells and of the anatomy of my specimens, I 

 satisfied myself that they belonged to two species of a new genus, which I propose to 

 call Jousseaumia, in honour of the French naturalist who first discovered this 

 Mollusc in the Aspidosiphon chamber of the two above-named corals. This new 

 genus and the two species may be defined as follows : - 



Jousseaumia, n. gen. 



Shell small, thin, triangular, equivalve, inequilateral, the anterior side the longer, 

 with numerous fine concentric ridges or striations ; umbones small, slightly 

 opisthogyrous. Hinge heterodont, with a somewhat elongately oval internal 

 ligament ; a single styliform more or less obtusely pointed cardinal tooth in the 

 right valve and two curved lamellate cardinal teeth in the left valve. Lateral teeth 

 somewhat distant, elongate, in the form of two ridges in the left valve fitting into 

 corresponding depressions in the right valve. Adductor impressions subequal, the 

 anterior impression somewhat elongated ; pallial line entire. Mantle largely open, 

 with a single pallial suture ; no pallial tentacles and no distinct siphons. The foot 

 elongate, liuguiform, geniculate, with a byssus consisting of a few long adhesive 

 threads ; a byssal groove on the posterior edge of the foot. Gills astartiform, 

 homorhabdic, non-plicate, with three or at most four rows of simple interfilamentar 

 junctions. Interlamellar junctions few, irregular ; the external demibranch wanting ; 

 the reflected lamella of the inner demibranch more or less developed, generally at the 

 anterior end of the gill only and attached to the sides of the foot. Hermaphrodite 

 and protamine. 



Jousseaumia heterocyathi, n. sp. 



The single cardinal tooth of the right valve bluntly rounded at its extremity, with 

 ;i narrower pedicle of attachment. The anterior cardinal tooth of the left valve well 

 developed, lamella curved posteriorly ; the posterior cardinal tooth a short, ill-defined 

 diverging ridge. Found only in Heterocyathus. 



Jousseaumia heteropsammis, a. sp. 



The single cardinal tooth of the right valve styliform, with a bluntly pointed 

 extremity and a broad base of attachment. The jjosterior cardinal tooth of the left 



