GYMNECHINUS EPISTICHUS. 289 



Gymnechinus epistichus, 1 sp. nov. 

 Plates 93, figs. 22, 23; 102, figs. 4, 5. 



The specimens are so nearly of a size that the measurements of the type will 

 answer for all. It is 26 mm. in diameter and only 12 mm. high, showing clearly 

 the flattened form of the test characteristic of the genus. The abactinal system 

 is 7 mm. in diameter along the axis IV-1 and nearly as much along the axis 

 V-2. The actinostome is a little larger, measuring 9 mm. across. There are 

 18 interambulacral plates in each column and 24 ambulacrals. The primary 

 spines are about 5 mm. long at the ambitus. The tuberculation of the test is a 

 characteristic feature for while there is, as usual, a primary tubercle on every 

 coronal plate, the secondaries are also prominent and form with the primaries, 

 at least on the mid-zone, nearly horizontal series. Thus on each interambulacral 

 plate at or just above the ambitus we have a series, consisting of a primary 

 tubercle in the middle and a pair of secondary tubercles on each side; at the 

 outer (radial) end of the plate, there are often two pairs of secondaries. In the 

 ambulacra, which are not nearly as wide at the ambitus as the interambulacra, 

 the secondary tubercles are few and irregularly scattered. The poriferous area 

 is moderately wide in the mid-zone, where the pores are fairly large, and the arcs 

 quite oblique, but actinally they become very narrow, the pores being small and 

 the arcs more nearly vertical. The genital plates (PI. 102, fig. 5) except 1 are 

 nearly of a size, decidedly higher than wide, and each carries two or three small 

 tubercles. Genital 1 is very small and carries no tubercle. The oculars are 

 about equal to each other and carry one to three tubercles apiece. Oculars I 

 and II are fully in contact with the periproct but the others are broadly exsert. 

 The periproct is not specially peculiar, but is covered by a dozen or more plates 

 of which the largest adjoin genital 3. The actinostomal membrane (PL 102, 

 fig. 4) is thin and perfectly bare, save for the buccal plates which are so small, 

 they scarcely exceed in diameter the tube-feet which they bear. The gill-cuts 

 are deep but are rather broad and not very sharply defined. The auricles are 

 low and do not meet across the ambulacra. The primary spines are moderately 

 stout, while the secondaries, though not much shorter, are very much more 

 slender. 



The pedicellariae are very similar to those of the other members of the genus. 

 The globiferous are rather rare and have valves (PI. 93, fig. 22) which measure 



1 iiri = in + trrfyas = a row, rank. 



