186 SILURIAN MOLLUSCA. 



two, with a simple pallial scar between them ; a strong internal 

 septum extends from before the beaks to the posterior margin 

 of the anterior adductor, forming a deep slit in the casts. Sur- 

 face generally smooth or nearly so. 



These palaeozoic shells have been confounded with Cucullma (by 

 Sow., PhilL, &c.), from which they differ in wanting the hood- 

 like plate of the posterior adductor, and having the septum in 

 the anterior end, and with Clidophorus (in Geol. Surv. of Great 

 Brit. vol. ii. pt. 2), from which they differ in having the hinge 

 crenulated as in Area. 



Tellinites affinis (M^Coy). 

 Sp. Char. Elliptical, moderately convex ; beaks small, about one- 

 third the length from the anterior end, which is elliptically 

 rounded, and with an undefined obtuse cardinal slope ; ventral 

 margin nearly straight, with a faint, shallow sinus in the mid- 

 dle ; posterior like the anterior end, rounded elliptically, with 

 sometimes an almost imperceptible flexure (as in Tellina) ex- 

 tending as a hollow in the left valve towards the beak from a 

 small sinus in the margin beneath the posterior end ; surface 

 smooth, or with a few obtuse marks of growth. Length 1 inch 

 4| lines, width (from beak to opposite margin) -^q^, length of 

 anterior end -^-j^^, depth of valve y^^ . 



This has almost exactly the shape of our recent Tellina radiata, 

 but the minute flexure above alluded to is in the longer end (which 

 in that species is the anterior). The species is most allied to the 

 Tellina ohliqua (Gold.) from the grauwacke of Ems, from which it 

 differs in being less transverse, in the beaks not being mesial, 

 and in the less angularity of the posterior slope; its greater 

 length, less central beaks, and concave ventral margin distin- 

 guish it from the NueuUtes subemarginata (Conrad) . 



Rare in the Upper Ludlow rock of Benson Knot, Kendal, 

 Westmoreland. 



{Col. University of Cambridge.) 



Area [Byssoarca) subcequalis (M^Coy). 

 Sp. Char. (Cast.) Oblong, equivalve, nearly equilateral, ends sub- 

 truncate, rounded, very gibbous in the middle, about twice as 

 long as wide ; depth of both valves equal to the width ; beaks 

 very large, obtuse, tumid, marked on the sides with four or 

 five large wrinkles ; a shallow sinus for the byssus in the ven- 

 tral margin a little nearer the anterior than the posterior end, 

 and slightly obliterating the simple pallial scar ; adductor im- 

 pressions deep, rounded; hinge-teeth very numerous, small, 

 equal, at right angles to the hinge-line. Width 10 lines, 

 length 1 inch 8 lines. 



