Bartsch — A New Classification of the Shipworms. 31 



bones project into the interior of the shell as a strong boss, from the under 

 side of which the slender blade curves downward basally. The narrow por- 

 tion of the blade is parallel with the inside of the shell. The median por- 

 tion is smooth, although it shows the groove that corresponds with the 

 external depression, and bears the usual knob at the ventral margin. The 

 posterior 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 pallettes are short stalked, the 

 stalk being more or less irregularly curved. The expanded blade is hollow 

 throughout its length, the cavity being divided into two chambers by a 

 median septum. 



The type and some additional specimens, Cat. No. 341,129, U. S. N. M., 

 come from a small piece of wood collected by the U. S. Coast Survey 

 Steamer Blake at Station 192, in 138 fathoms off Dominica, West Indies. 

 The type measures: length, 2.3 mm.; altitude, 2.2 mm. The pallette meas- 

 ures: length, 2.5 mm., of which 1.2 mm. belong to the stalk. Width of pal- 

 lette, 1.1 mm. 



XYLOPHAGA. 



An examination of the West American specimens belonging to the genus 

 Xylophaga Turton in the collections of the United States National Museum 

 shows that in addition to Xylophaga mexicana Dall we will have to recognize 

 two new species. The three species have quite distinctive characters, 

 and also occupy separate zoogeographic ranges. 



The exterior surface of the shell Xylophaga is not unlike that of Teredo and 

 Bankia but the posterior end does not gape and the posterior auricular por- 

 tion is not differentiated from the median. A broad median sulcus extends 

 over the exterior of the shell from the umbones to the ventral margin and a 

 strong lamina a little anterior to the middle of the sulcus reinforces the 

 shell on the inside. This lamina is marked at more or less regular intervals 

 by slight constrictions which give to it an articulated appearance. 



Xylophaga, like Teredo and Bankia, burrows in wood, but lacking the long 

 siphonal portion characteristic of those genera, the burrows are correspond- 

 ingly shallow. They are usually quite abundant and their burrows may 

 completely honeycomb and riddle the piece of wood affected. 



The following key will help to differentiate the species: 



Ridges on the anterior portion strong and distantly spaced . . washingtona 

 Ridges on the anterior portion not strong and distantly spaced. 

 Ridges on the anterior portion slender and closely spaced. 



Anterior median area broad mexicana 



Anterior median area narrow californica 



Xylophaga mexicana Dall. 



In Xylophaga mexicana there are twenty denticulated ridges to the milli- 

 meter in the center of the posterior area and the denticulated ridge bearing 

 posterior median portion is 1.7 mm. in width at the angle of the junction of 

 the posterior with the median part. 



