208 Mr. Gray's Conchological Observations. 



cal, somewhat spiral cones, the entrance to the digestive canal is 

 always placed on the side opposite to the ligament, which is con» 

 secjuently the front of the shell. The ligament on the other hand, 

 corresponds to the back of the animal, and is therefore the dorsal 

 side of the shell ; while the side opposite to the apices or umbones, 

 or that on which the valves open, is the basal ; for here the animal 

 protrudes its organ of locomotion, if it be provided with one, and 

 on this it crawls as on a base, and not on the other or dorsal line, as 

 I have heard some distinguished Conchologists assert, who attempt, 

 by this means, to explain the eroded appearance of the apices of 

 some of the fresh water species. As well might they, in fact, at- 

 tempt also to prove on the same ground that the fresh-water spiral 

 univalves crawl on their tips. On the same principle of constantly 

 referring to the animal in the description of the shell, the margin 

 of these bivalves will be divided into the anterior, or, according to 

 the excellent nomenclature recommended by Dr. Barclay, the 

 oral part ; the basal, or pedal j the posterior, or siphonal; and 

 the dorsal, or cardinal, parts : the intermediate spaces being de- 

 signated by a compound of these terms, as the anterior dorsal, the 

 anterior basal, &c. When the anterior dorsal part is impressed, I 

 use the term lunule to designate the depression ; and when the 

 same circumstance occurs on the posterior dorsal part, I apply to 

 it the name of escutcheon ; when the centre of this again is im- 

 pressed, Lamarck calls the depression the corselet ; these terms 

 are not novel, and are, at leasl, free from the objections which 

 attach to the older ones. Thus Avhen a bivalve shell is placed 

 on its basal margin, with the ligament towards the observer, the 

 light and left valve will correspond with his own sides. 



The bruchiopodous bivalves^ as the Terebratulae and Lingulae, 

 differ essentially from the true bivalves in their shells being sym- 

 metrical, or in other words formed of two symmetrical cones, as 

 well as in the different position which the animal assumes, a posi- 

 tion to which the Ostreae and Anomiae most nearly approach. The 

 sliell of the bruchiopodous bivalves is attached by its posterior 

 part, which is marked both by the hinge, and by the gap or per- 

 foration for the passage of the tendinous attachment : the opposite 

 end to this, is of course, tlic front of the shell. The perforated 



