62 
tion of that characteristic of both species: the ground colour is red as 
in esculentus, but the middle line of the ambulacra and inter- 
ambulacra form stripes of light, nearly white colour, as in Flemingii. 
in the same: work, Pårt, [I (pp: 18500 PL-IL Pigs, 19, 14,16), 
is described and figured a specimen supposed to be a hybrid 
between Spatangus purpureus anå Spat. Raschi; it ,,would on 
account of the high shape of the test decidedly be referred to 5. 
BRaschi; but the other characters (especially the subanal fasciole 
and the pedicellariæ) are quite those of purpureus. The petals 
are somewhat shorter than usual, especially the posterior ones", — 
Specimens intermediate between these two species were mentioned 
by Bell, who in his Report on the Echinodermata of a deep-sea 
trawling cruise off the S. W. Coast of Ireland, under the direction 
of Rev. W. Spotswood Green!) mentions ,,a fine series (of 
Spatangus Raschi) .... showing how very considerably this species 
varies, s0 much, indeed, that one is almost inclined to suspect 
that it forms hybrids with $. purpureus". 
Considerably more interest is attached to a supposed case of 
hybridisation between two West Indian Cidarids, Tretocidaris Bartletti 
(A. Ag.) and Stylocidaris affinis (Phil.). In the ,,Hawaiian and 
other Pacific Echini. The Cidaridæ"?) A. Agassiz and H. Lym. 
Clark make the remarkable statement that in Pretocidaris Bartletti two 
kinds of large globiferous pedicellariæ occur, which were otherwise 
regarded by me (Ingolf-Echinoidea) as characteristic of two different 
genera. H. Lym. Clark figures in his memoir ,,The Cidaridæ" ?) 
(Pls. 3—9) a specimen of Tr. Bartletti which differs conspicuously 
from the usual form of this species in having cylindrical and 
nearly smooth spines, while the typical form has tapering, thorny 
spines, the spinelets being developed only on the upper (adapical) 
side of the spines (comp. my paper ,,0On some West Indian 
1) Ann. Mag. Nat. Hist. 6 Ser. IV. 1889, p. 442. 
2?) Mem. Mus. Comp. Zool. XXXIV No. 1. 1907, p. 8. 
3) Bull. Mus. Comp. Zool. LI. No. 7. . 
