; Trans. Acad. Sci. of St. Louts 
TEREDO (TEREDO) PORTORICENSIS SP. NOV. 
Plate I, figs. 1-7. 
Shell subglobular, white, covered with a transparent, 
colorless: periostracum. The juncture of the anterior 
with the anterior-median area clearly marked by a 
broadly curved, slightly incised line. The ventral edge 
of the anterior area, forming an angle of about 100° 
with the anterior edge of the anterior-median area. 
Externally, the anterior area with the usual denticu- 
late ridges, the ventral posterior portion, with the ridges 
of about one-half the width of the intervening spaces. 
Dorsally the ridges are only one-fourth as wide as the 
spaces between them. Beginning at the ventral posterior 
edge, there are eight of these ridges to the millimeter, 
each ridge bearing approximately seventy denticles to 
the millimeter (fig. 1). The anterior-median area, at a 
point opposite the ventral edge of the anterior area, is 
one-quarter of the width of the entire median area. The 
denticulate ridges on this area, in a line continuous with 
the ventral edge of the anterior area, average twenty- 
five to the millimeter. In the type there are eleven of 
these ridges, which bear the usual broad denticles, there 
being twenty-eight denticles to the millimeter (fig. 2). 
The ventral ends of these ridges can be clearly seen 
continuing as sharp growth lines over the entire median 
area, but becoming less distinct on the auricle. The 
middle-median area is milk-white, in contrast to the 
semi-transparent anterior-median area, and is separated 
from the anterior-median area by a thin, narrow, trans- 
parent band. The posterior-median area is milk white 
and occupies one-half of the entire median area. The 
_ auricle is semi-transparent, showing more or less irreg- _ 
ular growth lines, and the periostracum is here thicker — 
than elsewhere on the shell. : 
