17 



(From Proceedings of the Academy of Natural Sciences of Pbilada., Oct. and Nov., 1863.) 



Description of a New Species of PLEUKOCEBA. 

 BY GEORGE W. TRYON. JR. 



Pledrocera plicatum, Tryon, t. 2, f. 6. 



Description. — Shell ovate-conical, spire attenuate, the upper whorls closely 

 plicate, the lower ones smooth or obsoletely concentrically striate. Whorls 

 but slightly convex, sutures well impressed. Color light green, with usually a 

 lighter band below the sutures, and ornamented with narrow or broad brown 

 bands. Aperture canaliculately produced ; outer lip thin ; columella twisted. 



Dimensions. L. -7, diam. -35 inch. 



Hab. Nashville, Tenn. 



Remarks. I owe to Dr. Gould the opportunity of describing this beautiful 

 little species. It differs from P. grossum, Anth., in being more slender, 

 different in color, and in having bands. The aperture is not nearly so large, 

 proportionally, and the plicje are finer. 



Description of a new species of TEBEDO, from New Bedford, Mass. 

 BY GEORGE W. TRYON, JR. 

 Teredo Thomsonii, Tryon, t. 2, f. 3, 4, 5. 



Description. — Valves convex, longer than wide ; the body rather stout. 

 Anterior auricle moderate, obliquely sub-triangular ; the posterior auricle 

 small, not very wide, short, somewhat reflected outwards. The dorsal margin 

 does not rise above the beak, and the basal margin does not extend so far 

 down the body, (which it joins almost at right angles,) as the anterior area. 



The transverse sculpture of the anterior area is sharply sculptured, and 

 becoming much more crowded towards its basal margin. The body, which is 

 surmounted by a narrow beak, and terminates below rather obtusely, has 

 the usual depressed narrow radiating area much more depressed than in the 

 other species, only obsoletely sculptured, and defined anteriorly by a quite 

 prominent rib. 



The separation of the posterior auricle is determined by a rather strong 

 sulcation. Internally, the shell is glossy and rather smooth ; the posterior 

 auricle overhangs, with a sharp, nearly straight projection. Immediately 

 above this it is concave, then convex ; and is marked by semicircular strong 

 growth lines. Beak with an oblique tubercle. Body with a well developed 

 depression corresponding to the radiating area outside. The usual internal 

 rib is scarcely developed, but the posterior tubercle is very prominent. 

 Apophysis thin, blade-shaped, a little wider at its termination, situated 

 obliquely to the direction of the body, with one edge turned slightly towards 

 it. Pallets obliquely, or sometimes regularly, obovate. The style is short and 

 directed backwards. The margins of the blade are convex, sometimes 

 regularly rounded, and sometimes heart-shaped at the end. From the style 

 an elevated ridge extends around a portion of each side of the blade, and is 

 smooth, while the centre, extending to the end, is Innately striate. The style 

 extends in the form of a lamina through the centre of the other side of the 

 blade. Tube notconcamerated, rather thick, and frequently much twisted. 



Hah. — Marine Railway and Cedar Buoys, Harbor of New Bedford, Mass. 



J. H. Thomson. 



Station. — Three or four feet below low water mark. 



Observation. — This new species of Teredo differs from all the others in the 

 very small proportionate size of the posterior auricle, and its not extending 

 basally as low down as the anterior area, in the depressed obsoletely sculp- 

 tured radiating area of the body, and the corresponding internal depression 



