314 Mr. W. Clark on the Pholadidse. 



As I have^ in the accounts below, entered so largely into the 

 incidents of this group, I shall at once plunge " in medias res." 



Pholas dactylus, Linnseus. 



Animal conically elongated ; body pale bluish white ; mantle 

 tinged with yellow, very thick ventrally, posteally, and around 

 the gape ; the other portions are of the thinnest texture, closed 

 throughout except anteriorly a large oval aperture for the passage 

 of the foot, and having the posterior end produced into a long 

 retractile sheath of a milk-white colour when denuded of the 

 epidermis, inclosing the branchial and anal siphons, which are 

 just separated at their termini, the former with 13-16 long cirrhi, 

 usually furnished on one side, sometimes on both, with 3-7 

 fimbrise, besides one or two intermediate shorter cirrhi, which are 

 ciliated on both sides ; the anal tube is plain and slightly escal- 

 loped, but in some states it appears to have a number of short 

 blunt cirrhi, which are not real, but occasioned by the doubling of 

 the points of the scallops on contraction ; their colour is brown, 

 interspersed with a few white blotches, producing a pepper-and- 

 salt appearance ; the sheath for a short distance from the ter- 

 minus is studded with subcircular whitish squamous papillae. 

 The foot is plain, hyaline, bluish white, suboval, pointed before 

 and behind, truncate basally, rather obliquely fixed to the body 

 by a long cylindrical, thick, fleshy white pedicle. The sheath can 

 be extended to double the length of the shell, and the branchial 

 portion is often distended with water to three times the usual 

 size ; its diameter greatly exceeds the anal one. There are on 

 each side the body a pair of long narrow symmetrical branchiae ; 

 these are nearly of similar size, reaching fully to the anterior end, 

 from which they taper gradually posteally, and lie, not free, but 

 fixed throughout their extent to within half an inch of the 

 branchial compartment ; they are pale brown ; the branchial ves- 

 sels are transverse, large, but not crowded, and present the aspect 

 of coarse pectinations. There are two triangular elongated 

 pointed palpi on each side in connection with each other and 

 the branchiae by narrow flat ribbons running above and below 

 around the mouth ; the structure and position of these palpi are 

 so unlike each other, that one can hardly admit the appellation 

 of palpum to be applied to the external one, which, instead of 

 being fixed to the body like its fellow, is glued by one side to 

 the mantle nearly its whole length, the point only being free, the 

 upper part forming with the upper portion of the one on the 

 other side an attenuated striated narrow band or fillet ai-ound the 

 upper part of the mouth ; these external palpi have the aspect of 

 very long irregular triangles, which, instead of being thick like 



