19 



grinding of their singularly formed jaws. The Saxicava 

 Rugosa has its projectile organ or tongue, a rough rasp- 

 like structure which may be supposed by repeated 

 application to be capable of wearing down the substance 

 of the rock; but in other boring animals, some of which 

 are naked, and perform the operation on the shells of 

 Bivalves, for the purpose of devouring the Mollusk within, 

 no such structure has hitherto been detected ; and the 

 Sasicaya Rugosa itself seems indisposed or incapable to 

 penetrate any other rock beside that of limestone. It 

 is probable therefore, that some digestive application 

 with chemical powers is first made use of, by which the 

 mechanical operation of the tongue is the more easily 

 secured. This slender organ is sometimes found protru- 

 ded, occasionally in a tortuous direction, in a passage 

 through the stone, to the length of nearly two inches, with 

 a transverse measurement not exceeding its own breadth : 

 a circumstance which seems to show, that the operation is 

 as much for obtaining food, as for the purpose of enlarging 

 its habitation. 



This species of Saxicava preserves its membranous covcr~ 

 ing while enclosed in its rocky cave ; but when, as is 

 sometimes the case, it has become enveloped in a mass of 

 coral, it becomes denuded, and so changed in form as 

 scarcely to be recognized. 



VENERIRUPIS. 

 GENERIC CHARACTER: The shell transverse, sides 

 unequal ; the posterior side very short, the anterior gaping 

 slightly. Hinge with two teeth in the right valve, and 

 three in the left, sometimes three in each, the teeth small, 

 approximate, parallel, and but little or not at all divergent. 

 Ligament external. 



* V. DECUSSATA. Venus Literata. Turt. Lin. Pen. 

 Brit. Zo., vol. 4, pi. 57, fig. 53. V. Decussata. Mont. 

 Test. Brit., vol. 1, p. 124. Stew. Elem., vol. 2, p. 382. 

 Venerupis D. Flem. Brit. An., p. 451. Common in 

 harbours through which a fresh stream flows. I have 

 obtained it from Looe, so near the surface of the ground, 

 that the muscles had fastened their byssus to it. This 

 and the following are termed hens, to distinguish them 

 from cocks or cockles. 



* V. PULL ASTRA. Venus P. Mont. Test. Brit., vol. 1, 

 p. 125. Venerupis P. Flem. Brit. An., p. 451. This 

 is by Sowerby consituted the type of the genus Pullastra. 

 It is common, though by several Naturalists strangely 

 overlooked or confounded with less common kinds. It 

 burrows, in rather firm ground, a few inches beneath the 

 surface, 



