Watt. — Uji Boltenia pachyderm atina. 335 



apertures, which are close together, are conspicuous, but not 

 prominent ; the oral aperture is more prominent than the 

 atrial, and is always directed towards the stalk. A charac- 

 teristic appearance is given to the members of this species by 

 the surface of the thick test being thrown into longitudinal 

 folds, of which there are, as a rule, two or three on each side, 

 with a distinct ventral fold. Very often the number on the sides 

 is unequal, there being probably two on the one side, one on 

 the other, with a ventral fold. Eound each of the apertures 

 there are three or four folds. The colour of the body-wall is 

 lodged in a thin external layer of the test, the remainder of its 

 thickness being of a glistening white. The body is sometimes 

 of a creamy-white colour which is sometimes streaked with 

 purple-brown, sometimes of a light-brown colour, or, again, of 

 a purple-brown streaked with white, or there may be a com- 

 bination of all three colours. In the young state the body is 

 generally creamy-white in colour. In harbour-water, where 

 the water is foul, the colour of the body is dirty-brown, and it is 

 covered with slime, often with a green growth which adheres 

 very closely to the surface of the test, and cannot be removed. 



B. Processes on Test. — In the young state, on the test there 

 are, as a general rule, spinous processes, which are often of 

 great length compared with the size of the body itself. 

 These, in many cases, are so numerous that the test is fairly 

 bristling with them. They generally disappear during growth, 

 but in a fairly large proportion of specimens which appeared 

 to be almost, or quite, full-grown (varying from 2iin. to 3^in. 

 in length), I found these spines present on the test. They 

 were, however, not numerous, and not large compared with 

 the size of the body. In many full-grown individuals, in place 

 of these spines there are on the test squarish or oblong 

 processes. 



In a number of specimens I collected I observed on the 

 test large protuberances, wdiich in some cases were almost 

 one-third or one-fourth the size of the animal itself. These, 

 W'hen examined, were found to be due to small bivalves (Cre- 

 ■nella discors, Lamarck ; Modiolacra ivipacta, Gray) imbedded 

 in the test. These were, on an average, a little over ^in. in 

 length. In some cases they were not completely covered. 

 The byssus was in all cases more deeply imbedded than the 

 shell, so that it appeared as if the mollusc had become at- 

 tached to the surface of the body by the byssus, and that the 

 irritation produced had caused the Boltenia to secrete fresh 

 layers of test-substance around it. Similar instances to this 

 are given in Sutton's "Evolution and Disease," p. 29. In 

 the cases where the lamellibranchs were not completely 

 covered by the test, they seemed to be still alive. When they 

 were completely imbedded there was, as far as I could make 



