32 



PHOLADIDiE. 



Fig. 858. 



T. Thomsonii. 



SO high as the beaks, nor extending so low down as the anterior 

 triangular process, concave externally and separated from the body 



by a well-marked groove, and forming at its 

 junction a rectangular sinus ; inner face over- 

 hanging the cavity of the beaks, fan-shaped, con- 

 cave, and concentrically striate. The anterior 

 marginal area is rather broad and very minutely 

 but deeply grooved, and separated from the rest 

 of the fang by a sharp ridge, across which are 

 rather distant, thin, erect, concentric laminas, one 

 for each groove, which fade off into the fine and 

 more numerous lines of growth. Beak with a medium sized, oblique 

 process. Tubercle at the point of the fang large. Sub-umbonal 

 blade slender, a little dilated at point, curved and presenting edge- 

 wise. Pallets battledore-shaped, the blades rounded, one face hav- 

 ing a narrow smooth rim enclosing a depressed, triangular, concen- 

 trically striate disk ; the other traversed by the style ; sometimes 

 a little emarginated at tip ; style a little oblique and slightly flex- 

 uous, about as long as the blade. " Tube rather thick, not con- 

 camerated." ( Tnjon.') 



Length, one fourth of an inch ; height, one third of an inch ; 

 sometimes much larger. 



Originally obtained by Mr. J. H. Thomson from Cedar Buoys 

 and the Marine Railway, New Bedford, where it lives in legions. 

 Also from Capt. N. E. Attwood, of Provincetown, who took it from a 

 whale-ship that had cruised in the West Indies. In its shape, auri- 

 cles, size, and markings, it is almost identical with Xylotrija bipin- 

 nata, but differs entirely in its pallets. It also very closely resem- 

 bles T. malleolus, a smaller species, but differs essentially in the 

 pallets also. 



Teredo dilatata. 



Diameters nearly equal ; wing large, not ascending so high as the beak, passing 

 off Irom the beak by a gentle slope, descending below the anterior triangle, hav- 

 ing no defining exterior groove, slightly concave and then reflected outwards on 

 the internal face. Pallets very small, battledore-shaped, end of tube concamerate. 



Teredo dilatata, Stimpson, Proc. Bost. See. Nat. Hist. iv. 113 (Oct. 18.51) ; Shells of K 

 Eng. 26. — Adams, Genera, ii. 33.3. — Tufts, Proc. Essex Inst. i. 26. — Tkyox, 

 Proc. Ac. Nat. So. xiii. 464 (1862). 



" Valves white, polished ; length and breadth equal ; anterior 

 [triangular] area with fine, concentric, somewhat divergent striae, 



