394 TELLINID.E. 



with rapidity, the latter operation being effected by a 

 series of jerks. The tubes are capable of great exten- 

 sion ; the larger or imbibing one is sometimes as long 

 as the shell is broad, and thrust out in every direction 

 as if in search of food. 



"Montagu considered it the young of P. vespertina, 

 which is invariably a flatter and more oval shell. Pay- 

 raudeau seems also to have mistaken the two ; the pre- 

 sent species is probably his P. fragilis. It is the P. 

 florida of Turton, but not of Lamarck. 



( 4v . 2. P. COSTULA'TA *,(Turton) N f \<\l> 



P. costulata, Turt. Conch. Dith. p. 87, t. 6. f. 8 ; F. & H. i. p. 279, pi. xix. 

 f . 5. 



BODY milk-white, delicately suffused with pink: mantle 

 having thickened edges, which, project beyond the valves in 

 front and at the sides, and are slightly cirrated, especially at 

 the posterior end : incurrent (or lower) tube very long, cylin- 

 drical, and octangular ; each angle is clothed with a row of 

 minute cilia and terminates at the orifice in a tooth-like 

 point: excurrent (or upper) tube conical, contracted at the 

 orifice, which is plain and covered with eight longitudinal rows 

 of cilia like those of a Beroe; both tubes diverge from each 

 other at a right angle, the lower one being straight or but 

 slightly bent, and the other (which is much the shorter of the 

 two) turned upwards : foot flexible and pointed. 



SHELL resembling that of P. tettinella, var. gmcilis, in almost 

 every respect but the peculiar sculpture of the posterior slope. 

 Instead of this part being simply marked by minute or deli- 

 cate longitudinal striaa, it has from twelve to twenty strong 

 and sharp thread-like ribs, radiating from the beaks to the 

 outer margin in each valve, which is consequently scalloped or 

 notched ; this ribbed area is distinctly defined, and separated 

 from the comparatively smooth portion of the surface. The 

 shell is also of a thinner texture ; the colour of the rays is 

 deeper and usually purple, but not so regular ; the streak on 

 the anterior side of the beak is broader and more like a patch ; 

 and the posterior side is rather broader and more truncate. 

 L. 0-45. B. 0-75. 



* Slightly ribbed. 



