170 MUSEUM NOTES. 



a short note (with a figure) in Science Gossip for i8g6 (Vol. III., 

 N.S. p. 147). 



Mr. Kennard says that at Heme Bay it is by far the most 

 abundant mollusc, " living in burrows, about six inches deep, in 

 the London Clay. Associated with it is the well-known form, 

 Pholas Candida which it (superficially) closely resembles, but the 

 Pholas is by far the rarer. It is probable that the Petvicola will 

 be the cause of the greater denudation of the foreshore, since its 

 burrows break up the London Clay, and thus enable the waves 

 to act in a more destructive manner than hitherto. There can 

 be no doubt that the mollusc has been established at Heme 

 Bay for many years, and that it has been overlooked through its 

 outward resemblance to Pholas Candida. It may readily be 

 distinguished by the fact that the latter form possesses only one 

 siphon, whilst Petvicola pholadifovmis has two, and it was this 

 which first drew my attention to it. I believe that the species 

 will eventually become a common denizen of those parts of our 

 coast where there is a suitable habitat."' 



The accompanying figures of Petvicola are copied from the 

 Report of the Invevtehvata of Massachusetts, by Dr. A. A. Gould, 

 edited by W. G. Binney (Boston, 1870). Although at first glance 

 the resemblance to Pholas Candida is striking, it really belongs to 

 the Veneridse, a family most members of which are very unlike 

 Petvicola superficially. The animals differ; in Pholas the respira- 

 tory siphons are united nearly to their ends ; in Petvicola they are 

 united only at the base. Pholas Candida has a small plate (or 

 additional valve) over the hinge line and the ligament is not 

 visible externally. In Petvicola the valves fit close at the hinge, 

 and there is a strong external ligament. 



The habits of Petvicola in America are similar to those 

 described above by Mr. Kennard. Dr. Gould says "On various 

 parts of our coast ; at Chelsea and Nahaut beaches it is found 

 abundantly, imbedded in jutting fragments of a marsh which 

 once existed there, but which ha: '^een washed away by inroads 

 of the sea, and now only an occasional remnant lifts its head 

 above the surrounding sand. Also found in great quantities 

 boring into hard blue clay, at low-water mark on Phillip's 

 Beach." 



It is an interesting biological question, how came it about 



1 A. S. Kennard in lift. 



