112 BIOLOGICAL SOCIETY OF WASHINGTON. 



larly dotted with sporadic calyces, composed of circular gastro- 

 pores, each surrounded by a circle of five to nine dactylopores, with 

 occasional sac-shaped ampullae, which are most abundant on the 

 most elevated projections of the surface, and almost entirely absent 

 from depressed parts. Diameter of the dactyloporic circle about 

 i.o 11 . ; of the central gastropore about 0.3 7 mm . ; the distance from 

 center to center of the calyces varies from 1.5 to 2.5 mm . 



Gastropores, cup-shaped, shallow (o.25-o.5o mm .), smooth inside, 

 with the tip of a white spiculose nipple-shaped, or roundly conical 

 style in the bottom of each, projecting about its own diameter or 

 less into the cup through the aperture of a long nearly vertical 

 conical tube which it occupies and closely fills. The length of 

 this style, which resembles a fox's brush, is nearly equal to the 

 thickness of the ccenosteum. The margin of the cup in fully de 

 veloped gastropores is simple and entire, and depressed slightly 

 below (or in no case elevated above) the general surface. In im 

 mature calyces there is frequently a shallow groove running from 

 the innermost point of each dactylopore toward or into the gastro 

 pore. 



Dactylopores variable in number, eight seeming to be the normal, 

 but seven the most common number, never sporadic, in well-de 

 veloped calyces entirely separated from the cavity of the gastropore 

 throughout their extent ; in immature ones joined to it by a shallow 

 superficial groove. Transverse section a little ovoid, the wider arch 

 away from the gastropore, and marked by a vertical, narrow, spongy 

 lamina forming the style. The exterior margin simple, not elevated 

 above the general surface, but rather slightly depressed below it. 

 Neither sort of pore shows tabulae. Ampullae, simple sac-shaped 

 cavities as large as, or larger than, the calyces, not protruding above 

 the general surface, but more numerous on the prominences of the 

 crust. 



General surface between the above-described openings imper 

 vious, nearly smooth, with the vermicular fine reticulations of the 

 ccenosteum structure showing through the translucent substance, 

 and giving the surface a granular look, a vertical section of the crust 



