MONOGEAPH OF AMERICAN SHIPWOEMS. 21 



TEREDO (TEREDO) MORSEI, new species.^ 

 MORSE SHIPMORM. 



Shell subglobular, white. The extreme anterior portion with the 

 usual sinus and reflected smooth callus at its external border, the 

 main portion bearing the dental ridges, which radiate from the 

 anterior margin, where they are closely crowded, backward to the 

 junction with the posterior median portion. Forty-seven of these 

 ridges are present in the type. At their posterior extremity they 

 are separated on the early turns by spaces that are about five times 

 as wide as the ridges, while in the last third they are separated by 

 spaces no wider than the ridges. These ridges slope a little more 

 abruptly on the dorsal side than on the ventral, and are finely den- 

 ticulated at the free border. The anterior median portion is rather 

 broad and marked with rather closely spaced, strongly denticulated 

 ridges, of which there are 27 in the type opposite the ventral border 

 of the anterior portion. The middle median portion is slightly 

 concaved, marked by rather rough curved lines of growth. The 

 posterior median portion is about as broad as the anterior and 

 median portion combined, marked by distantly spaced rough lines 

 of growth, between which finer lines are apparent. The posterior 

 auricle is large, strongly curved and slightly upturned at the poste- 

 rior border. It extends strongly up toward the umbone. On the 

 inside the umbones are strongly marked and from the lower edge 

 a conspicuous blade extends for a little more than half the length 

 of the shell. A moderately curved, decidedly broad and slightly 

 twisted blade extends for a little more than half the length of the 

 shell from the under side of the umbone. The junction of the ante- 

 rior and middle portion is marked by a raised thread, while the 

 auricle is reflected over the posterior median portion as a thick callus, 

 and is free as a slender shelf at its anterior extremity. The pallets 

 are rather broad at the anterior termination of the calcareous por- 

 tion. The corneous portion is rather short and deeply cut. The 

 sides of the calcareous portion slope gently toward the somewhat 

 curved and twisted stalk. 



The type, Cat. No. 346333, U.S.N.M., measures : Height, 5.7 mm. ; 

 length, 6.3 mm.; diameter, 5.5 mm. The pallets measure: Length, 

 5.1 mm., of which 1.7 mm. go to the stalk; diameter, 1.7 mm. 



The tj^pe and a number of additional specimens were obtained by 

 Mr. T. G. Townsend at Manhattan Beach, Long Island, New York. 



This species closely resembles Teredo {Teredo) navalis^ but dif- 

 fers from it in having the ridges of the anterior area more numerous 

 and much more closely spaced. The specimen of Teredo navalis 



3 This species was discovered after the manuscript of this paper was in galley form and 

 therefore does not appear in the key. 



