AMBLYPNEUSTES PACHISTUS. 327 



Ambulacral plates not very numerous (31 or 32 in specimens 

 34 mm. in diameter) about 30-50 % more numerous than in- 

 terambulacral; primary tubercles very small, those of am- 

 bulacra near ambitus occupying about one half the height 

 of plate and those of interambulacra occupying about one 



third the height of plate griseus. 



Ambulacral plates numerous (40-43 in specimens 34 mm. h. d.) 

 about 50-70% more numerous than interambulacral; pri- 

 mary tubercles large, those of ambulacra occupying almost 

 the entire height of plate, especially actinally, where they 

 form a rather crowded vertical series; those of interambul- 

 acra occupy about one half the height of plate .... pachislus. 

 Poriferous areas narrow, the two together forming only one third 

 of ambulacrum; vertical diameter .ti5-.75 of horizontal; tuber- 

 culation relatively coarse; test and primaries pale brown . . gram/is. 

 Ambulacra broader than interambulacra; pore-pairs in three very distinct vertical 



series . Iriseriatus. 



Amblypneustes pachistus, 1 sp. nov. 



Plates 104, fig. 6; 112, figs. 10-11; 121, figs. 1-3. 



There are in the M. C. Z. collection eleven specimens of Amblypneustes which 

 are easily distinguished from griseus and ovum by their much stouter tests and 

 coarser tuberculation. While it is possible that they are only a form of griseus, 

 they are so easily distinguishable, it seems better to give them a name, and 

 describe and figure them. The largest (PI. 112, figs. 10, 11) is 48 mm. in diame- 

 ter and 34 mm. high. The actinostome is 15 mm. across, while the abactinal 

 system is only two thirds as much. There are about 34 interanibulacral and 54 

 ambulacral plates in each column. The spines are practically wanting. A 

 somewhat smaller specimen is 30 mm. in diameter and 25 mm. high, and has the 

 actinostome 11 mm. across. There are 25 interambulacral plates in each column 

 and no less that 39 ambulacrals. The spines are present, in some numbers, 

 and the largest primaries, just below the ambitus, are 4 mm. long. In a speci- 

 men 21 mm. h. d., there are 22 interambulacral plates, and more than 40 ambula- 

 crals, in each column. 



The test is well arched and rather high, the vertical diameter ranging from 

 .70 to .80 of the horizontal. The coronal plates are all low and wide. At the 

 ambitus, each interambulacral plate carries a primary tubercle, somewhat nearer 

 the ambulacral than the median suture. On the inner side of this tubercle 



very coarse or stout. 



