ECHINUS ANCHISTUS. 271 



Echinus anchistus, 1 sp. nov. 

 Plates 93, figs. 8, 9; 103, figs. 4, 5; 111, figs. 1-3. 



The greatly flattened test is the most striking feature of this southern species 

 and serves to distinguish it at a glance from its neighbor, euryporus. The 

 largest specimen at hand (PI. Ill, figs. 1-8) is 23 mm. in diameter but only 

 9.5 mm. high; the height is thus .41 v. d. In smaller specimens the height is 

 relatively greater and in the smallest specimen (7 mm. in diameter) it is a trifle 

 over .50 h. d. The abactinal system is about .30 h. d. and the periproct is more 

 than half of that. The actinostome is about equal to the abactinal system. 

 In the largest specimen there are 12 interambulacral and 18 ambulacral plates 

 in each column, while in the smallest the numbers are 8 and 10 respectively. 

 Although the type has 18 ambulacral plates, there are only 9-11 primary tubercles 

 n each half-area, and in the little specimen only 6 or 7 can be counted. The 

 pore-pairs are small, the arcs nearly vertical and the poriferous areas very nar- 

 row, particularly at the peristome, in striking contrast to the condition in eury- 

 porus. The coronal plates at ambitus are fairly well covered with secondary 

 and miliary tubercles but abactinally they become barer. They are not at all 

 rough and the areolse are not depressed nor are the bases of the tubercles notice- 

 ably elevated. The ocular plates (PI. 103, fig. 4) are all excluded from the 

 periproct by the wide genitals, and both sets of plates carry many small tubercles. 

 The periproct is covered by relatively few, rounded, flat plates, among which 

 the suranal is very prominent. None of these plates carry tubercles. In the 

 type the plates are so few and scattered that the periproctal membrane is plainly 

 visible among them, but this is not usually the case. The actinostomal mem- 

 brane (PL 103, fig. 5) contains numerous small and thin plates distal to the buccal 

 circle, but none of them bear any pedicellarise. The gills are very small and the 

 gill-cuts are almost wanting. 



The primary spines are slender and fragile, when unbroken about half as 

 long as the test diameter, smooth and even polished, but showing clearly numer- 

 ous longitudinal striations. The smallest primaries are not so smooth and the 

 very slender secondaries, which are not numerous, are distinctly rough (under a 

 lens) particularly at the tip. 



Pedicellaria? are common but not abundant. The globiferous are found 

 chiefly on the ambulacra. The valves (PL 93, figs. 8, 9) are very similar to 



= nearest of kin. 



