90 

 MARINP] ANIMALS. 



MOLLUSCA.— Part II. 



BY O, S, ROUND, ESQ. 

 ( Continued from page lb.) 



It was impossible in my first paper on this class of Marine Animals to do 

 more than touch the different genera, amplified as the list has been of lato 

 years by the addition of an order of beings not hitherto comprehended within 

 its limits, but which more modern naturalists have, and I think very justly, 

 decided to belong to the same great family, and which from their compara- 

 tive frequency of occurrence amongst us, possess something like a peculiar 

 claim on our attention. I speak of the ^'Conchifera," of which the Oyster 

 and Mussel, {Mytilus edulis,) are examples. Both these are so common that 

 it would seem almost a work of surplusage to describe their conformation; 

 and yet common as they are, there are very few, I believe, except purely 

 scientific men, who are able accurately to describe their various parts, and 

 indeed in some of these, modern discovery has been, and still continues to 

 be active. 



Now with regard to the first, we know and perceive it is true, that it is 

 covered with a laminated shell, or a bivalve that is composed of layers, formed 

 chiefly of calcareous matter; but what the minute conformation of those layers 

 is, is probably still to be learned. On examining this shell, the microscope 

 shews that it is perforated throughout like a fine cullender in the minutest 

 conceivable manner; and that as these layers are formed, these perforations 

 take a substantive form, and piled, one upon the other, constitute at length 

 separate prismatic bodies, capable of being detached from each other, and 

 forming a series of cellular formations, which are nearly in a direct course 

 from the exterior to the interior of the shell, appearing, when under a great 

 magnifying power, a series of hexagonal figures not unlike the plates of the 

 shell of the Tortoise, (Testudo.) These are most apparent in the large species 

 of Oyster which is so common in our markets during nearly the whole 

 year, and which is captured chiefly on the French coast; this species being 

 so large that the eye can almost detect the formation I have alluded to, 

 and with ease the vai'ious degrees of development of the lamina and the 

 calcareous deposit interspersed, and the vacancies yet unfilled. What is termed 

 'mother of pearl,' is so named from being the surface on which the pearls 

 are usually found, and is a coating, in some sort, membraneous, lying in folds, 

 and which, when spread, loses the colour, which arises in fact from a repetition 

 of faint hues, probably of a green tendency, which produce optically the pink 

 or crimson hue, which, as is well known, is the complimentary colour to the 

 other, or that which the edges, or colourless adjacent portions of a green 

 object always exhibit. All the Oyster tribe exhibit this cellular structure of 

 the shell, and where, as sometimes happens, there is a tubular structure lying 



