108 IOWA STUDIES IN NATURAL HISTORY 



southern Florida coast, while at the other extreme of the West 

 Indian region, on Buecoo Reef, Tobago, it is more abundant than 

 at any other place where I have personally seen it. 



CENTROSTEPHANUS RUBICINGULUS' Sp, UOV. 



Plate I, figs 1 and 2. 



Test 12 mm. in horizontal diameter, 5 mm. high, decidedly 

 flattened both above and below. Coronal plates 8 or 9 in each 

 column, with no essential difference between ambulacra and 

 interambulacra in this particular, but the interambulacra are 

 about 4 mm. wide at ambitus while the ambulacra are scarcely 

 3.5. Abactinal system large, 5 mm. in diameter, covered with 

 a fairly thick skin ; all the oculars are insert; genital plates 

 large, each with a long genital papilla, the length of which about 

 equals the width of the plate; periproet about 2.3 mm. across,, 

 covered with small roundish plates, set in thick skin. Uppermost 

 abactinal primary spines, usually two of each vertical series, 

 very small (1 mm. long, more or less), smooth and club-shaped; 

 all the other primaries, especially those of midzone which are the 

 longest (12-14 ram.), very rough with the usual rings of minute 

 spinelets. Peristome 7 mm. in diameter, quite closely covered 

 with non-ambulacral plates among w^hich the five pairs of buccal 

 plates are easily distinguished by their larger size and their 

 clusters of pedicellariae and the spinelets so characteristic of 

 CentrostepJianKs. 



Pedicellariae of only two kinds so far as observed, ophiceph- 

 alous and globiferous. The former have valves .25-.40 mm. 

 long, with the loops 10-30 per cent more. These pedicellariae 

 occur on the buccal plates and scattered about sparsely on the 

 test ; those on the test are considerably larger than those on the 

 peristome. The globiferous pedicellariae, as in the other mem- 

 bers of the genus, have the valves imbedded in heavily pigmented 

 glands; these pedicellariae therefore, though very small, are 

 made conspicuous by their black tips ; the valves are .22-.32 mm. 

 long and terminate in 4 short, subequal, somewhat spreading 



' Rubus — red -j- cingulus = a zone or band, in reference to the banded spines. 



