4GG PROCEEDINGS OP THE ACADEMY OP 



broad, the anterior area moderate, the posterior narrow and extending above 

 the beaks. 



Anterior auricle with its dorsal margin declining concavely from the beak 

 to a lateral angle, whence its basal margin extends rather convexly and ob- 

 liquely downwards to its junction at an angle with the body, the point of junc- 

 tion being horizontal with, or slightly below that of the posterior auricle, and 

 at about two-fifths the length of the shell from its apex. 



The lateral margins of the fang are, anteriorly very slightly concave, pos- 

 teriorly convex, and the ventral termination is infolded, forming a strong 

 internal tubercle. 



Posterior auricle quite narrow, being about three times as long as its width, 

 reaching in typical specimens slightly above the beaks ; its posterior margin 

 is very oblique and curved, following the direction of the fang. Beaks ele- 

 vated, not wide. 



Internally, the shell is quite concave, with the auricles but little reflected, 

 the posterior one marked by a shell-like ridge extending over the body. Apo- 

 physis oblique, slanting posteriorly, strongly clavate at its termination. Dor- 

 sal margin somewhat lamellar, becoming prominently elevated at the beaks, 

 where it is crowned by a tubercle. 



Color white, glossy ; the anterior area elegantly concentrically sculptured, 

 the anterior side of the body ornamented with the usual narrow radiating and 

 decussately striated area, posterior to which the surface gradually becomes 

 smooth. 



The tube is semi-concamerated, and very fragile. 



The pallets are widely different from those of any other species, the blade 

 being very transverse, much broader than long and widest at the apex, which 

 is a horizontal sinuous line : both lateral margins are generally angularly con- 

 vex, rapidly diminishing to the short compressed stalk. The stalk, instead of 

 continuing in the same plane as the broad side of the blade, is deflected from 

 it at an obtuse angle. 



T. megotara, Hanley. 



T. megotara, Hanley, Brit. Conch, i. p. 77, t. 1, f. 6, and t. IS, f. 1, 2. 

 Jeffreys, Ann. & Mag. Nat. Hist. 3d ser. vi. p. 121. Sowerby, Must. 

 Brit. Shells, t. 1, f. 3. 

 nana, (part.) Fischer, Journ. Conchyl. 2 ser. i. p. 136. Gray Ann. & Mag. 

 Nat. Hist. 2 ser. viii. p. 386. 



oceani, Sellius, Hist. Nat. Tered. 



Brurna deWoceano, Vallisnieri, Op. Phys. Med. 



Hob. England. 



Coll. Acad. Nat. Sciences. 



Description. Valves about as wide across the auricles as their length, the 

 body rapidly attenuated to the base. The anterior auricle is moderate and 

 subtriangular ; the posterior is dilated, very large, and rising above the beak, 

 while its basal margin extends below the line of that of the anterior area. 



The anterior area nearly approximates in form to that of T. N o r v a g i c a and 

 joins the body below, at right angles. The posterior auricle exhibits a marked 

 difference from that of the last-named species ; its dorsal margin is so very 

 concave in form as ordinarily to exhibit an approach to three-fourths of a circle, 

 the highest posterior point of which is curved forwards somewhat, so that the 

 dorsal apex of the auricle points anteriorly and extends above the beak. 

 From this highest point the margin posteriorward is obliquely declining and 

 moderately convex in outline to the extreme posterior extension, (which is 

 considerably below the middle of the auricle) whence it sweeps around very 

 convexly, joining the fang or body considerably below the middle of the valve, 

 and below the line of the base of the anterior area, by a somewhat rounded 

 angle. The anterior lateral margin of the body is directed posteriorly, and is 



[Sept. 



