490 



PROCEEDINGS OF THE ACADEMY OF 



[Aug., 



gent in sculpture as well as in other particulars that a glance is 

 sufficient to separate the two. They agree in the characters upon 

 which I have founded the present subgenus, but otherwise do not seem 

 to be remarkably close. For the sake of comparison, a few notes 

 upon the latter species are appended. 



Mopalia (Dendrochiton) heathii Pilsbry. PI. XL, figs. 1, 2, 3, 7. 



Mopalia heathii Pilsbry ('98), p. 288. 



Mopalia heathii Keep ('04), p. 350 (merely listed). 



Mopalia heathii Thiele ('10), pp. 108, 109. 



Shell small, oblong, elliptical, wide in relation to its length, 

 carinated, rather elevated, the side-slopes nearly straight. 



Valves wide and short, little beaked; the lateral areas not raised, 

 ill defined; central areas without sculpture 2 save the very fine, 

 even, rather distant granulation which covers the whole surface. 

 Posterior valve with semicircular posterior outline, the mucro 

 anterior in position; posterior slope concave, but not so steep as 

 in M. thamnopora. 



3 



Mopalia heathii. — 4. Outline of entire animal. 5. Large lateral tooth of the 

 radula. 6. Girdle spines. 7. Outline of interior of tail valve. 



Anterior valve with 8 slits; intermediate valves with 1,1; last 

 valve "ischnoid," with a regular crescentic insertion plate cut by 

 5-8 slits. In the intermediate valves the insertion plates are con- 

 tinuous across the sinus. 



2 Pilsbry writes: "The intermediate valves very faintly radially trisulcate 

 at the sides," but my specimens exhibit this feature with difficulty. 



