112 PIIOLADID.^. 



crenulatus. Perhaps it is the P. callosa of Lamarck 

 from the neighbourhood of Bayomie. His diagnosis, 

 and especially the words " valvarum callo cardinali pro- 

 minulo globoso/' are more applicable to P. parva than 

 to P. dadylus. It certainly is his P. dactyloides. Al- 

 though the very specimens which he thus described 

 were received by him from Dr. Leach as the P. parva 

 of Montagu, he capriciously rejected that name, and 

 substituted an inappropriate one of his own. It is 

 the P. ligamentina of one of the earlier works of 

 Deshayes, and Anchomasa Pennantiana of Leach. 



C. Shell oval ; valves furrowed lengthwise : dorsal shield single, 

 placed centrally, extremely small and triangular. Zir- 

 phcea, Leach. 



4. P. crispa'ta"^, Linne. 



P. crispaia, Linn. S. N. p. 1111 ; F. & 11. i. p. 114, pi. iv. f. 3-5. 



Body very thick, reddish-brown : tubes long, encircled with 

 branched papillte : sheath velvety : palps much smaller than in 

 the other species : foot oval. 



Shell convex with a slight depression in the middle, soHd, 

 and of a coarse and rugged aspect ; it is divided into two 

 nearly equal parts by a rather broad furrow, which runs 

 obliquely from the beak in each valve to the front margin : 

 sculpture, about 20 longitudinal rows of imbricated prickles, 

 formed by the intersection of the ribs with numerous trans- 

 verse scalloped ridges; these markings are on the anterior 

 side only, and do not extend to the separating furrow ; the 

 rest of the surface is nearly smooth, or exhibits the usual 

 irregular lines of growth: colour dull white with a slight 

 tint of yellow : epidermis whitish, becoming brown towards 

 the edges, wrinkled obliquely, and leaving its impress on the 

 surface of the shell: margins acutely angular or beaked at 

 the anterior end, with a very wide heart-shaped gape towards 



* Curled. 



