TRIBE PHOLADARIA. V 



trically striated : dorsal edge posteriorly reflected and inflated : 

 with two anterior, dorsal, sub-ovate, accessory valves ; the epidermis 

 anteriorly running down upon two flattened valves and then a cal- 

 careous tube conspicuous at the extremity. t, 9 . . 1-fV — W. Colum- 

 bia. Very like Papyracea: the intermediate ages without the tube. 



P. Papyracea.* Turt. B. p. 2. t. 1./. 1 to 4.— Sow. G.— 

 Reeve, t. 24. f. 3. — W. S. t. \. /• 1. Ovate oblong, closed and 

 very obtuse posteriorly, open and truncated anteriorly, posterior mar- 

 gin reflected at the hinge into a thin nearly erect narrow plate ; 

 dirty white, divided by a longitudinal groove ; anteriorly with de- 

 pressed concentrical lamellse, posteriorly towards the hinge with close 

 obliquely curved toothed thin ridges, the remaining portion nearly 

 smooth : nacreous white within. — Young. (P. Lamellata. Turt„ 

 Biv. t. \.f. 5, 6. — W. S. t. 1. f. 2.) — Without the smooth space 

 at the posterior ventral edge, and consequently with a large oval 

 gape. \\. — England. 



P. Curta. Sow. Z. P. 1834. Oval, anteriorly acuminated, 

 posteriorly rounded : valves divided by a transversely grooved band ; 

 the posterior area obliquely divided, the dorsal portion with radia- 

 ting wrinkles and transverse striae, the ventral thinner and sub- 

 inflated : anterior surface with concentric strise : accessory valve 

 solitary, posterior dorsal, sub-acuminated at the ends and con- 

 tracted in the middle : upper and lower edges with a horny testa- 

 ceous epidermis which on the dorsal surface is anteriorly forked. 

 t^h 2 — W, Columbia. 



P. Cornea. Sow. Z. P. 1834. Oblong, thin, posteriorly 

 rounded, anteriorly obtuse : a thin horny epidermis ; valves divided 

 by a band ; posterior area obliquely divided, the dorsal portion 

 being rather rugose, the ventral smooth : anterior surface larger 

 and smooth ; with three accessory valves, the posterior dorsal one 

 rounded, and sub -emarginated anteriorly : anterior gape large. 5 - I -^. 

 — W. Columbia. 



P. Tuberculata.* Turt. B. p. 5. t. 1. /. 7, 8. — W. S. t. 

 l.jf. 3, Oblong with the ventral margin posteriorly sinuated, but 

 not forming a beak at its extremity ; gape nearly orbicular : the 

 transverse rough strise disappearing anteriorly after crossing the 

 longitudinal groove : a single accessorial valve and a rough tubercle 

 on the edge above the teeth, f . . 1 J. — England. 1 



1 In this genus we must include. Turton's 



XYLOPHAGA. 



Orbicular, cequivalve, inequilateral, posteriorly gaping, with two 

 sub-triangular testaceous accessory pieces, a 'minute cardinal 



