242 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



Interior of valves calloused. Anterior valve with 9 strong, 

 distinctly cut insertion teeth, the 3 anterior concave, and all 

 coarsely grooved on their outer surfaces; slits 8 in number, their 

 porous apices connected with the apex of the valve by lines of 

 minute pores. Central valves with wide, gently arcuate sutural 

 laminae, scarcely if at all connected across the rather deep sinus ; 

 slits 1-1. Posterior valve with a barely indented flattening in- 

 stead of a posterior sinus ; slits 1-1. Eaves distinctly spongy. 



Girdle of moderate width posteriorly, broadening in front to 

 the wide lobe characteristic of the genus, so that the maximum 

 diameter of the animal is in the region of the head (text figs. 

 3-4). To the naked eye or under lenses of moderate power the 

 girdle appears smooth and nude over its entire area dorsally^ 

 save for a marginal palisade of minute hyaline spinelets, and 

 three or four submarginal series of armored chsetse, the mem- 

 bers of the inner series of which are conspicuously the largest 

 and extend clear around the girdle, about 12 chaetse in this series 

 encircling the anterior lobe, the remainder placed 1 opposite 

 each suture and 2 directly behind the tail valve. The ventral 

 surface of the girdle is clothed with very minute scattered 

 spinelets, visible only under quite a high power. In dried speci- 

 mens the girdle becomes excessively thin and leathery. The 

 ventral surface of the anterior lobe shows no evident radial 

 striation even under moderate magnification. 



Color of shell in alcohol, a warm brownish red with more or 

 less lighter painting, except the anterior portion of the head 

 valve which is uniformly paler. Girdle brownish buff, the an- 

 terior lobe sharply paler. Interior of shell tinted a soft salmon 

 flesh. 



Precephalic lobe of mantle with 7 large digitations and a 

 number of smaller ones. 



Ctenidia 21-22 on each side. 



Measurements of type (in alcohol) : 



Maximum length of animal 32.7 mm. 



Maximum width of animal 26 mm. 



Length of anterior lobe (dorsal) 8 mm. 



Length of shell alone 22.5 mm. 



Width of fourth valve inside girdle 16 mm. 



^That it is actually thus devoid of spines I am not prepared to state. 



