Proceedings of the British Association, 241 



lately examined a recent Terebratula preserved in spirits, and ascer- 

 tained that the perforations in the shell, before described, were filled 

 up in the living animal by membranous coeca, containing cells, form- 

 ing, as he considered, a glandular apparatus, though its connection 

 he had not yet been able to trace. He then described the structure 

 of those bivalve mollusks, in which the mantle is more or less closed 

 as being generally less characteristic than that of the families already 

 described, their texture being apparently more homogeneous ; and the 

 membranous residuum, left by the action of acid, being less distinct. 

 Frequently, however, traces of a cellular origin were to be seen in 

 shells whose general texture was most homogeneous : sometimes it 

 was seen in the shell, and not in the decalcified membrane, and 

 frequently in the membrane when no traces of it were visible in sec- 

 tions of the shell. Hence Dr. Carpenter felt himself justified in 

 regarding all shells as originating in the secreting action of the cells 

 forming the superficial layer of the mantle ; these cells remaining 

 persistent and separate in some cases, whilst in others they coalesced. 

 The peculiar tenacity of the cellular membrane in Pinna and its allies 

 was attributed to the presence of an intercellular horny matter, 

 between the true cell-walls ; the same substance being elsewhere thrown 

 out upon the surface of the layer, as an epidermis or periostracum. 

 Among the shells under consideration in the present report, those 

 of the family Myida were particularly distinguished by their evident 

 cellular structure ; the genus Pandora formerly referred to as one of 

 the most aberrant and exceptional in the structure of its shell, was 

 now shown to be connected with the surrounding families by Mya, 

 Thracia, Anatina, and other genera of Myida, whose characters were 

 of an intermediate nature. In the class Echinodermata, Dr. Carpenter 

 extended and confirmed the results he had before given respecting 

 the minute structure of their skeletons, which preserve a remarkable 

 conformity throughout the group, extending to the small calcareous 

 plates met with in the Holothuridse. Dr. Carpenter had also ascer- 

 tained that the same minute structure existed in the Nummulite with 

 the small existing foraminifera described by Ehrenberg ; but that the 

 supposed nummulites brought by Mr. Pratt from Bayonne presented 

 several forms of structure entirely distinct from that of the true num- 

 mulite. — Mr. Charlesworth thought that extreme caution should be 



