36 BULLETIN 122, UNITED STATES NATIONAL MUSEUM. 



concentric wavelike markings, and so placed upon the dorsal pos- 

 terior median portion that about one-third projects inward and two- 

 thirds outward. On the exterior there is a deep inflexion at the 

 junction of the auricle with the posterior median part. The interior 

 is bluish white. The junction of the anterior and median part is 

 marked by a mere slightly raised thread, while the middle median 

 portion is marked by a strongly impressed groove. The auricle ex- 

 tends inward as a shelf, as already indicated. The umbones are 

 marked by a strong knob. The base of the ventral median part is 

 broken in the type. 



The type, Cat. No. 17622, U.S.N.M., comes from St. Vincent, West 

 Indies. 



It measures: Height (estimated), 11 mm.; length, 9.5 mm.; 

 diameter, 9.5 mm. 



This species differs from Teredo (Teredora) thoinsoni Tryon in 

 having the anterior median area much narrower than in that species. 

 It can be differentiated from Teredo {Teredora) panamensis by its 

 much broader, entire median portion. It comes nearest to the Euro- 

 pean Teredo {Teredora) inalleolus Turton as far as shell characters 

 are concerned, agreeing with this in the width of the denticulated 

 anterior median portion, but differs from it in having the denticu- 

 lated ridges of the anterior portion much more distantly spaced. It 

 is also quite possible that when the pallets of it will be found, addi- 

 tional characters will be presented. 



This is probably what Jeffreys referred to as Teredo malleolus 

 Turton, sent to him by P. P. C^^rpenter from the West Indies. The 

 specimen is marked as having been determined by Jeffreys. 



PsiLOTEREDO, new subgenus. 



In this subgenus the auricle fuses with the posterior median por- 

 tion on the inside in such a manner that no shelf projects. In fact, 

 in some of the species it is difficult to note even a suture. The pallets 

 are spoon-shaped, with the outer distal portion slightly excavated. 



Type. — Teredo dllatata Stimpson. 



KEY TO THE AMERICAN SPECIES OF PSILOTEEEDO. 



Pallets : 



Blade elongate ovate stimpsoni. 



Blade not elongate ovate. 



Blade ovate jamaioensis. 



Blade not ovate. 



Blade broadly ovate. 



Lateral margin of base of blade convexly rounded. 



Strong concentric markings restricted to nail tryoni. 



Strong concentric markings not restricted to nail knoxi. 



Lateral margin of base of blade not convexly rounded. 



Lateral margin of base of blade almost straight_s/fife/-/"oosi. 

 Lateral margin of base of blade slightly concave dilatata. 



