Bulletin 26 92 



Dimensions. — Diameter, 27.75 mm-', height, 21.5 mm.; 

 apical disk, about 11 mm.; peristome, 12 mm. 



Description. — Test of medium size, elevated, subpentagonal 

 in outline, the ambulacral areas being at the angles, while the 

 interambulacral areas form the sides. The superior surface is 

 inflated or domed, whereas the inferior surface is abruptly rounded 

 from the ambitus to the peristome. 



The ambulacral areas are prominent, nearly straight, in- 

 flated, and gradually tapering from a point at their junction 

 with the oculars to the peristome where they are 5.5 mm. wide. 

 Above the ambitus, there are only scattered tubercles or granules, 

 but the surface is impressed by fine, longitudinal, undulating 

 ridges giving it a shagreen appearance. Extending over about 

 two-thirds of the distance from the peristome to the ambitus, 

 there are two rows, of about seven each, of round, noncrenulate, 

 imperforate, mammillated, alternating tubercles which decrease 

 in size toward the peristome. Adradially of these, are two rows 

 of small granules in each pore area. The row near the outer edge 

 of the area has from three to eight granules, and is shorter than 

 the more median row which extends nearly as far toward the 

 ambitus as do the mammillated tubercles. Small granules en- 

 circle the areolas, and, associated with these are almost micro- 

 scopic crenulations or warts which form a delicate wreath about 

 the base of each scrobicule. Above the ambitus, the pores are 

 both round and oval. Each pair of pores is located in a depres- 

 sion, surrounded by a peripodium, and arranged in arcs of three 

 pairs to each ambulacral plate. Below the ambitus, the pore 

 pairs increase in number till there are four rows at the peristome. 

 In this region, the pores are more oblique than those above the 

 ambitus, and emerge from the sides of a granule which separates 

 the pores of each pair. Encircling each pore pair is a well de- 

 veloped rim which is interrupted opposite the pore nearest the 

 peristome. 



The interambulacral areas are large, depressed at the middle, 

 and about three times as wide as the ambulacral areas. The 

 surface above the ambitus is ornamented like that of the am- 

 bulacral areas. Below the ambitus, there are four rows of round, 



