DOROCIDARIS BLAKEI. H 
system (PL II. Figs. 1, 2) which would undoubtedly lead to their being con- 
sidered specifically distinct. Yet, if the isolated huge fan-shaped radioles 
had alone been dredged, radioles (PI. II. Figs. 7-10) nearljMdentical in shape 
with those of the Jurassic Rhabdocidaris remus De.s. (Phyllacanthus Br.) few 
palseontologists would have hesitated to refer them to that genus. 
A comparison of the differences in the test of this species and of D. iMpU- 
lata shows that the coronal plates (PI. II. Fig. 1) have a comparatively larger 
and more elliptical scrobicular area, surrounded by a single row of larger 
secondary tubercles ; the tubercle and boss are much smaller, and the tuber- 
culated spaces of the median interambulacral area are also narrower. In a 
specimen measuring 37 mm. there are 6-17 primary interambulacral plates, 
while in a smaller specimen of D. papilkda, measuring .S.5 mm., there are 7-8 
primary interambulacral plates. In the ambulacral ai-eas the poriferous zone 
is nearly as broad as the median ambulacral spaces (PI. II. Fig. 1), while in 
D. papilkda it is narrower ; the secondary ambulacral tubercles are also 
smaller than in that species. It also differs from D. pui^illala in having a 
smaller anal system, but this is covered by a larger number of plates inside 
the outer row (PI. II. Fig. 2) than in D. papillata. The ornamentation of the 
radioles is the same on the long fusiform, or cylindrical, or the more or less 
fan-shaped radioles of the test (PI. II. Figs. 3-10); these figures show well the 
gradual passage from a long, sharp-pointed, cylindrical radiole (PI. II. Fig. 3) 
to a huge fan-shaped radiole (Fig. 10), through the successive stages of Figs. 
4-9, in which the radioles become little by little more flattened and spread- 
ing at the extremity. As the radioles become more fan-shaped, the rows of 
spinules are gradually changed into minute serrations, spreading more and 
more, and becoming somewhat less prominent towards the extremity, rows of 
smaller serrations being intercalated as the extremity of the radioles becomes 
more and more fan-shaped. The broad end of the fan-shaped radioles is 
sometimes slightly concave. 
In the first specimens of this species, dredged by Captain Sigsbee, there 
were no radioles showing the intermediate stages here figured between 
the long, sharp, cylindrical radioles of Plate II. Figs. 3, 4, and such fan- 
shaped ones as are figured in Plate II. Figs. 9, 10. Enough has been 
shown from the examination of this species to show how little we are as 
yet able to determine among the Cidaridse the value of either generic or 
specific characters. Before we can hope to make the much needed accu- 
rate revision of this family we need a large mass of material, especially 
