122. = Dr. T. Wright on a new Genus of Fossil Cidaride, 
area, stop short at the equator, or between the equator and the 
disc ; the intertubercular space on the upper surface of the test is 
therefore in general wide, and covered with a small miliary gra- 
nulation. The apical disc is large ; the genital and ocular plates 
are expanded and foliated. The mouth-opening is of moderate 
dimensions, and the peristome is divided into ten nearly equal- 
sized lobes. The spines are long, slender, and needle-shaped ; - 
those that are known, equal at least the diameter of the test, and 
their surface is sculptured with delicate longitudinal lines. 
Hemipedina is related to Diadema in having the pores ar- 
ranged in the zones in single pairs and the tubercles perforated ; 
but it is distinguished from Diadema by the absence of crenu- 
lations on the summits of the mammillary eminences. It is 
related to Pedina in possessing perforated and uncrenulated 
tubercles ; but it is distinguished from that genus in having the 
pores in the zones in single pairs (Pedina having the pores in 
triple oblique pairs hke Echinus), in having the elements of the 
apical disc more largely developed, and in the species being nearly 
all small and depressed forms. Hemipedina is related to Echin- 
opsis in possessing uncrenulated and perforated tubercles, with 
the pores in pairs ; but it is distinguished from the latter by the 
narrowness of the ambulacral areas, the depressed form of the 
test (Echinopsis being high and inflated), the form of the mouth- 
opening, and the deep decagonal lobes of the peristome (that of 
Echinopsis being almost deprived of these incisions), together 
with the greater size and development of the elements of the 
apical disc. 
Hemipedina, as far as we at present know, is composed of 
Jurassic species, which commence in the lower Lias and extend 
into the Coral Rag, each stage possessing its own specific forms. 
The following synopsis of the British species now before us will 
be figured and described in detail in our Monograph on the 
British Oolitic Cidaride. 
A. Species from the Lias. 
Hemipedina Bechei, Wright. 
Cidaris Bechei, Broderip, Geol. Proc. ii. 202. 
Diadema Bechei, Agassiz, Morris’s Catalogue of British Fossils, 
Ist ed. p. 51. 
Test small, much crushed, and covered over with spines ; ambu- 
lacra with two rows of tubercles; interambulacra with four 
or six rows of tubercles ; spines long, slender and needle- 
shaped, 7{,ths of an inch in length, with longitudinal lines on 
