MOLLUSCS. 



257 



marks the limit of the thickened edge of the mantle, and in one large group of shells 

 a portion of the pallial line makes a re-entrant angle. This is the pallial sinus and is 

 found only in bivalves with a siphon, 

 where it marks the place of attachment 

 of the muscles of that organ. 



The classification of the acephalous 

 mollusca is still in a very unsatisfactory 

 condition. In the system of Lamarck 

 the group was divided into two sub- 

 classes, based upon the number of ad- 

 ductor muscles, those in which only one 

 of these muscles was present forming 

 the Monomyaria, while those with two 

 were called Dimyaria. Woodward, who 

 wrote one of the most valuable manuals 



of conoholosjy which has as vet ap- fig. 266. — Ijiner surface of left valve of Cj^Wierca.-n, impres- 



^•' ./I giQj^ Qf anterior adductor; c, cardinal tootli of hingo; 7i, 



peared, used the presence or absence hinge ligament; l, palUal line; ;;, posterior adductor; s, 



, . „ ,. . . pallial sinus; ^, lateral teetli of hinge; u, umbo; a7,lunule. 



01 siphons as a means ot division, those 



where no siphon was formed being the Asiphonida, the others forming the Siphonida. 

 The Siphonida in turn were subdivided, according to the presence or absence of a pal- 

 lial sinus, into the Sinupallialia and the Integropalliala, respectively. With each of 

 these systems many grave faults may be found, and hence, for our purpose we will 

 divide the Acephals directly into families, without the intervention of sub-classes and 

 orders, and other intermediate divisions. 



In economic importance the Osteeid^e, the oyster family, stands pre-eminently 

 first. The characters of the family, taken in its older and broader sense, are as fol- 

 lows : The two valves of the shell are unequal, the hinge is without teeth, and, as a 

 rule, the single adductor is nearly median in its position. The two halves of the 

 mantle are free from each other, and the borders are fringed with small tentacles, and 

 the foot is rudimentary or even entirely absent. 



The genus Ostrea has a shell so irregular that specific limits are very poorly 

 defined. The left valve, which is attached to some submerged object, is hollowed out 

 to receive the body, while the upper right valve is nearly flat. With us Americans, 

 Ostrea virginiuna is the important form, and to it most of the succeeding account 

 applies. In Europe the species which form the bulk of those eaten are O. edulis and 

 0. angulata. 



Ostrea virginiana extends, on our Atlantic coast, from the Gulf of St. Lawrence 

 to the Gulf of Mexico. In the former region the oysters are found from the Bay of 

 Chaleur to Prince Edward's Island. The beds are small and in many places seem to be 

 decreasing. The oysters found here are usually large. These beds are separated 

 from the nearest natural living beds to the south, by a thousand miles of coast line, 

 but between these points evidence is abundant that in former times the gap was far 

 less, for remains of extinct beds are found all along the coast, from Mount Desert 

 Island to Cape Cod. At Damariscotta, Maine, was once a large bed which furnished 

 the Indians with the means of many a feast. Here, year after year they came, and 

 with the refuse shells they formed huge heaps which to-day are the delight of the 

 archaeologist. The oysters in these "kjokkenmoddings" (a Danish term meaning 

 Jieaps of kitchen refuse) were of enormous size, one having been found at Damarisr 



VOL. I. — 17 



