MONOGRAPH OF AMERICAN SHIPWORMS. 23 



TEREDO (TEREDOTHYRA) DOMINICENSIS Bartsch. 

 DOMIMCA SHIPWORM. 



Plate 21, fig. 2 ; plate 33, fig. 1. 



Teredo (Teredothyra) doniiniccnsi^ Bartsch, Proc. Biol. Soc. Washington, 

 vol. 34, pp. 30, 31. 

 Shell subglobiilar, compressed, cream yellow, the extreme anterior 

 portion bearing a notch, whose external border is reflected as a smooth 

 fold over the outer portion of the shell, but not appressed to it. Im- 

 mediately back of this are the dental ridges, which appear to radiate 

 more or less fanlike from the anterior margin. They are closely 

 crowded at the anterior margin, but become regularly more distantly 

 spaced as they pass from the anterior to the posterior termination. 

 At the latter place they are about two and a half times the width of 

 the ridges. These ridges are exceedingly finely denticulated at their 

 free margin ; 34 of these are visible, but this is not all, for the earliest 

 are partly covered by the anterior reflection, and some have probably 

 been lost by the erosion of the umbones. These ridges join the dental 

 ridges of the anterior median portion in a little more than a right 

 angle. The latter are very closely crowded, the spaces between them 

 being mere impressed lines. The dental ridges of the anterior me- 

 dian portion are a little more strongly denticulated than the dental 

 ridges on the anterior portion. In about the middle of their length 

 they separate from their closely packed condition, taking a decidedly 

 backward slant on the early portion of the shell and a lesser angle 

 on the last portion. The middle of the median portion is but a 

 roughened groove, which extends from the umbone to the ventral 

 margin. The posterior portion is about twice as wide as the anterior 

 and median and is marked by rather strong lines of growth. In fact, 

 it would almost seem as if the attenuated dental ridges, after bending 

 over the median groove, continued as smooth raised threads over the 

 posterior median portion. The median portion, compared with 

 Teredo in general, is rather narrow. The posterior portion forms a 

 moderately large auricle, which on the external surface is marked 

 by lines of growth and a few roughened ridges. The interior of the 

 shell is bluish white. The umbones project into the interior of the 

 shell as a strong boss, from the underside of which the slender blade 

 curves downward basally. The narrow portion of the blade is 

 parallel with the inside of the shell. The median portion is smooth, 

 although it shows the groove that corresponds with the external de- 

 pression, and bears the usual knob at the ventral margin. The pos- 

 terior auricle does not project into the cavity of the interior to form 

 a shelf, but fuses smoothly with the median portion. The auricle 

 shows lines of growth markings on the inside. The pallets are short 

 stalked, the stalk being more or less irregularly curved. The ex- 



