FHOLAS. 109 



species differs from P. dactylus in its more convex 

 shape and thinner texture ; the front gape being much 

 narrower ; not having any dorsal cells, nor more than 

 a single shield; and in possessing a strong and remark- 

 able fold on the hinge-plate. 



The specific name was given by Lister. Spengler 

 described aud figured the present species as the P. 

 papyraceus of Solander ; but his description, quoted by 

 Spengler, is more like that of a young P. crispata. It 

 is also the P, dacty hides of Delle Chiaje, and Barnea 

 spinosa of Risso. The P. cylindrica of J. Sowerby, 

 from the Red and Coralline Crag, appears to be inter- 

 mediate between the present species and the next. 



3. P. parva*, Pennant. 



P. parvus, Penn. Brit. Zool. iv. p. 77, pi. xL f. 13? P. parva, F. & H. 

 i. p. Ill, pi. iv. f. 1,2, pi. ii. f. 2, and (animal) pi. F. f. 3 & 3 A. 



Body oval, milk-white : mantle invested at its edges by a 

 thin membrane : tubes marked inside lengthwise with alternate 

 brown and white stripes ; orifices scalloped, but neither are 

 cirrous ; sheath thick, reddish-brown, covered with nume- 

 rous granular papillae ; these become larger towards the ex- 

 tremity of the sheath, which is encircled by a fine pile or 

 fringe : foot oval when at rest, rounded in front and pointed 

 behind when protruded, and attached by a long cylindrical 

 fleshy stalk. 



Shell oblong, somewhat compressed, rather solid : sculpture, 

 very numerous transverse rows of imbricated and flexuous 

 ridges, which are puckered or flounce-like on the crests formed 

 by the intersection of slight and less numerous longitudinal 

 ribs ; these markings are more crowded on the anterior side, 

 and in the adult gradually disappear towards the posterior 

 side, which is smooth or only exhibits some irregular lines 

 of growth ; there are seldom prominent and sharp prickles as 

 in the preceding two species : colour white, sometimes slightly 

 stained with brick-red from the matrix in which the shell is 

 imbedded : epidermis light-yellowish and irregularly fibrous, 



* Small. 



