CLASS XII. 

 CONCHIFERS (CONCHIFERA^. 



WITH LAMARCK we unite all the "bivalve molluscs in a single 

 class, which also contains the Brachiopoda of CUVIER. They are 

 acephalous molluscs, of which the mantle is always more or less, 

 and often entirely, cloven into two laminse, and which are covered 

 by a bivalve shell. Their respiratory apparatus is external, and 

 situated either between the mantle and the body in form of plates, 

 or in the substance of the mantle itself. 



The intestinal canal, very various in length, is closely sur- 

 rounded by the other viscera. The oesophagus is short, or there 

 exists no oesophagus obviously distinct. Ordinarily a stomach is 

 present, yet in Ligula the intestinal canal is almost of the same 

 width throughout; and in Orbicula also a stomachal expansion is 

 not apparent. Salivary glands are not present in the Lamelli- 

 branchiata ; in the Bracliiopoda it is doubtful whether one of the 

 glandular masses, that surround the intestinal canal, is to be 

 regarded as a salivary gland 2 . Largely developed on the other 

 hand is the liver, which, as in the rest of the invertebrate animals, 

 receives arterial blood alone, and has no gall-bladder. Numerous 

 lobes, consisting either of blind sacs or of branching coecal tubes, 



1 Most of the general works on this class treat also of the rest of the molluscs, and 

 have been partly cited above. Here belongs especially the great work of POLL Com- 

 pare besides, the article Conchifera, of DESK AYES in TODD'S Cyclopaedia of Anatomy and 

 Physiology, i. 1836, pp. 694 716, and R. GARNER, On the Anatomy of the lamclli- 

 branchiate Conchifera, Trans, of the Zool. Soc. n. i, pp. 87 101, PI. 18 20. 



2 In Ligula Anatina CUVIER observed a difference of colour in these glandular 

 masses, which led him to consider the round white gland, situated in the middle, to be 

 salivary, the lateral, divided into many lobes, and yellow brown, to be a liver. OWEN 

 could not perceive such difference of colour in Lingula Audebardii, and supposes that, 

 in the specimens examined by CUVIER, it was to be ascribed to some accidental cause, 

 as bleaching by the spirit in which the animals were kept (Trans. Zool. Soc. I. p. I5/)- 

 I must, however, observe that the specimen examined by me gave the same results as 

 CUVIER has noticed, although I do not regard difference in colour as a certain proof of 

 difference in function. In the other genera of Brachiopoda, which I have not examined; 

 Terebratula and Orbicula, OWEN found no glands except the liver. 



