266 



BULLETIN 100, UNITED STATES NATIONAL MUSEUM 



Description. — The test is rather low, flattened both above and 

 below, sometimes less so above where the apical system may be some- 

 what elevated so as to give the test a subcorneal appearance. The sides 

 are more or less arched. The circumference is circular or sub- 

 pentagonal. 



The ambulacra are rather distinctly sinuate. The interporiferous 

 zone is about twice the width of a pore zone. The marginal series of 

 tubercles is very regular, the tubercles being small and inconspicuous 

 and not nearly contiguous; there are usually some small miliary tuber- 

 cles between each two consecutive marginal tubercles. Within the 

 marginal tubercle each plate usually carries one smaller tubercle at 

 the lower edge of the plate and often in addition one placed higher 

 up and nearer the midline of the zone. When only the lower one of 

 these tubercles is present, a fairly distinct vertical series is formed 



Fig. 10.— Apical system of Goniocidaeis (Cyrtocidaris) tenuispina, new species. Male (a) and 



FEMALE (6). X6 



within the marginal series; when two inner tubercles are present the 

 vertical arrangement is obscured. There is a rather conspicuous, 

 naked, somewhat sunken middle part, and in general the ambulacra 

 have a rather naked appearance. The horizontal grooves are fairly 

 conspicuous, though merging into the sunken median part. The pores 

 are equal sized, not sunken, separated by a rather narrow wall which 

 rises into a fairly conspicuous tubercle; the ridge separating the 

 adjoining pore pairs is low and inconspicuous. (PL 73, figs. 5-6.) 



In the interambulacra the areoles are not very deep; the 3 or 4, 

 rarely more, proximal ones are confluent; at most some of the small 

 proximal ones are slightly transverse-oval. The scrobicular ring of 

 tubercles is not very conspicuous; the tubercles, however, are dis- 

 tinctly larger than the marginal ambulacral tubercles. There is a 

 rather broad, sunken, naked median part, leaving room for only a 



