32 BULLETIN 122, UNITED STATES NATIOI^AL MUSEUM. 



not quite as wide as the ridges. In fact, the bases of the adjacent 

 ridges touch each other. The sides of the dental ridges slope a little 

 more abruptly dorsally than ventrally, the free edge being rather 

 conspicuously denticulated. Of these ridges, 97 are present in the 

 type. The anterior median portion is very broad and bears denticu- 

 lated ridges which are separated by mere impressed lines. These 

 ridges are a little more closely approximated than those of the an- 

 terior area, and a little narrower than those of the anterior area. 

 They join these at almost right angles. The central median portion is 

 slightly depressed. The anterior border is strongly marked off from 

 the anterior portion by a conspicuous line. The posterior median 

 portion is about as wide as the anterior, and is marked b}^ rough, 

 curved growth lines. The posterior part forms a rather conspicuous 

 auricle, the junction of which with the posterior median portion 

 forms a depressed groove. The interior is bluish white. The junc- 

 tion of the anterior and median portion is not conspicuous. The 

 central median portion is a slightly roughened groove, which bears a 

 prominent knob at its ventral extremity. The posterior portion pro- 

 jects over the median part to form a strong shelf. The blade, which 

 is broad and grooved and extends to about half the length of the 

 shell, is pendant from below this heavy umbone. We have been 

 unable to obtain pallets of this species so far. 



The type and a lot of other specimens. Cat. No. 344661, U.S.N.M., 

 is Z 1402 from greenheart timber in fresh water in Mira Flores Lake 

 at Pedro Miguel, Canal Zone, collected by Mr. C. J. Embree, office 

 engineer, the Panama Canal. The type measures : Height, 11.3 mm. ; 

 length, 11.6 mm. ; diameter, 12 mm. 



This species is most nearly related to Teredo {Neoteredo) reyneiy 

 the only other known species of the subgenus, but differs from it in 

 having the auricle much larger and in not having the posterior por- 

 tion of the median part bend down suddenly. 



This is the only Teredo so far reported from the fresh waters of 

 America. 



Subgenus Teredora Bartsch. 



1921. Teredora Baetsch, Proc. Biol. Soc. Washington, vol. 34, p. 26. 



In this subgenus the auricle is so placed upon the posterior median 

 portion that half of it projects as a shelf inwardly, and the other half 

 outwardly. The pallets have a naillike depression, which may be 

 marked by concentric lines of growth, or these may become even rib- 

 like, and it may have longitudinally radiating riblets, confined to the 

 basal portion of the naillike part, or these also may be strong and 

 riblike. 



Type. — Teredo malleolus Turton. 



