MONOGEAPH OF AMEEICAN SHIPWORMS. 35 



is marked by a tumid line, while the iniddle median portion shows as 

 a groove that extends from the umbones to the knob at the ventral 

 margin. The posterior area is shaped like a pallet, with a stalk 

 pointing to the umbone and so attached to the posterior median part 

 that as much of the shelf thus formed projects inward as there is 

 auricle projecting outward. The blade is almost cylindric, slightly 

 expanded at the basal margin, and curves through about half of the 

 length of the shell. The pallets are paddle shaped, the free stalk 

 being short, but it appears to extend through the center of the blade, 

 the inside of which is smooth. The basal portion of the blade is solid 

 and thick, while the distal portion is naillike, and is marked by a se- 

 ries of longitudinally radiating ribs which are connected and crossed 

 by fine concentric riblets. 



The type and some additional specimens. Cat. No. 212591, U.S.N.M., 

 were collected by the United States Bureau of Fisheries steamer 

 Albatross in Panama Bay at Station 2805, in 51^ fathoms. 



It measures : Height, 4.6 mm. ; length, 3.3 mm. ; diameter, 5.5 mm. 

 The pallet measures: Length, 4.8 mm., of which 1.3 mm. go to the 

 stalk, and 2.3 mm. diameter. 



The curious pallet and the extremely limited number of dental 

 ridges distinguish this from all other American shipworms. 



TEREDO (TEREDORA) VINCENTENSIS, new species. 

 ST. VINCENT SHIPWORM. 



Plate 27, figs. 1 and 2. 



Shell large, white. The extreme anterior portion with the usual 

 sinus which shows a strongly reflected callus, free at its posterior 

 margin. From this cavelike portion the dental ridges pass abruptly 

 downward and then backward in an even curve. They are very dis- 

 tantly spaced at the posterior margin, where the spaces that separate 

 them are probably seven or eight times as wide as the dental ridges. 

 The dental ridges slope a little more abruptly on the umbonal side 

 than on the ventral. Most of them show a slender secondary thread 

 at the basal margin. Of these ridges, 26 are present in the type, 

 and none are here covered by the callus. It is therefore a perfect 

 specimen. The anterior median portion bearing the narrow dental 

 ridges which are here separated by mere impressed lines is narrow. 

 The dental ridges join those of the anterior portion at almost a right 

 angle. The middle median portion forms a slightly depressed groove 

 which is crossed by rough wrinkles. The posterior median portion 

 is about twice as wide as the anterior and the middle median part 

 combined, and is marked by a series of wavelike markings which 

 are extensions of those marking the middle portion of the median 

 part. The posterior part is exceedingly oblique and placed far on 

 the dorsal margin. It is pallet-shaped and marked by a series of 



