TEREDO. 31 



and subdivided by a delicate line, barred with minute lines and by 

 more distant raised ridges, wliicli are the terminations of the lines 

 on Hie anterior fang-area ; remainder of fang smooth 

 or with minute lines of growth. Posterior auricle 

 as liigh as or generally higher than the beaks, from 

 which it is separated by a narrow and deep rounded 

 sinus ; it is broad and regularly revolute without 

 any external furrow to mark its boundary, or any 

 overhano-ing internal shelf, terminating in a shal- 

 low obtuse sinus at about the lower third of the 

 valve, inner face witli distinct concentric stri^. There are from 

 twenty to thirty radiating grooves on the triangular area, and as 

 many on the anterior marginal area, where they are closely 

 crowded and beautifully decussated. The pallets are small, 

 rounded or emarginate at tip, widening to an angle on each side, 

 one angle a little higher than the other, then concavely narrow- 

 ing into a short, pointed stalk. Tube solid, not chambered. 



Diameters, one fourth to one half of an inch. 



Many specimens occurred living in a floating pine board covered 

 also with large specimens of Anati/a, found at Newport, R. I. Others 

 were obtained at New Bedford ; also at Provincetown in cedar buoys. 



The broad, uprising, revolute wing with no defining groove ex- 

 ternally and no shelf internally, its lower junction being much 

 lower than that of the anterior triangle, with the deep, narrow, 

 rounded sinus between the wing and the beak, are the chief char- 

 acteristics. It is now considered as distinct from T. nana^ Turton, 

 otherwise that name would take precedence. T. denticulata, Gray, 

 seems to be a large elevated form of the same. 



"o"- 



Teredo Thomsonii. 



Shell large, claw long, posterior auricle short, not ascending so high as the 

 beak nor descending so low as the anterior triangle, externally defined by a shal- 

 low groove, and internally overhanging the cavity of the beaks and concentrically 

 striated. 



Pallets ovate-triangnlar, with a short style, with a marginal rim on one side en- 

 closing a deep triangular cavity concentrically striate, and a central rib on the other. 



Teredo Thomsonii, Tryox, Proc. Acad. Nat. So. Philad. (Oct. 1863), p. 28, pi. 2, figs. 3, 4, 5. 



Yalves higher than long ; anterior auricle obliquely sub-triangu- 

 lar, inclining upwards, rather large, coarsely and deeply grooved 

 radiately ; posterior auricle small, rolling outwards, not ascending 



