CONCHOLOGY. 
compressed, with 13 contiguous unequal valves, 
the lower side ones less, 
Lepas scalpellum, 
CLASS III.—CONCHIFERA. 
Body without articulations or transverve seg 
ments, without visible head or eyes, and always 
inclosed in a bivalve shell. 
A.- Without permament ligament. 
11. Pholas. Shell transverse, oval, equivalve, 
open at one end, mostly furnished with variously 
shaped accessorial valves behind. Hinge with a 
long curved tooth in each valve placed under the 
hind margin : lateral teeth none. 
Includes the whole of the Pholas tribe. 
12. Teredo, Shell orbiculer, hemispherical, equi« 
valve, ending in a long cylindrical tube which is 
furnished at the end with variously shaped valves, 
Hinge with a long curved tooth in each valve 
within the margin ; lateral teeth none. 
13. Xylophga, Shell, like the last, lodged in 
wood, very open befure and closed behind, but 
is without the long cylindrical tube and_ its 
accessorial valves, and wants the teeth within 
the margin, 
B. With the ligament external, 
14, Saxicava, Shell transverse, equivalve, une 
