from the Lias and Oolites. 33 
face of both is covered with minute granules nearly as large as 
those which adorn the other parts of the test. The madrepori- 
form tubercle makes a distinct elevation on the surface of the 
single plate, and the anal aperture is transversely oblong; the 
base is flat, the mouth-opening is small, and its margin is divided 
into ten nearly equal-sized lobes ; the spines are unknown. 
Affinities and differences.—In its general outline and depressed 
upper surface, with the pedal pores in nearly a single file, this 
little Urchin resembles a Diadema ; from that group however it 
is distinguished by the rudimentary condition of the ambulacral 
tubercles, and the absence of crenulations from the summits of 
the mammillary eminences. It is distinguished from P. Bakeri 
by having small primary tubercles set more closely together, and 
in having a greater number in each row. From P. aspera it is 
known by having the upper surface more depressed, the pedal 
pores separated by a moniliform line of granules, and in the 
absence of secondary tubercles. It has a strong resemblance at 
a first glance to Diadema Moorei, but an examination with the 
lens at once discloses the points of difference, which are these :— 
the ambulacral areas in Pedina Etheridgu have imperforate gra- 
nules on their upper parts, whilst in Diadema Moorei there are 
perforated tubercles; the moniliform line between the pedal 
pores in P. Etheridgit is absent in D. Moorei; the mouth- 
opening is likewise much smaller in P. Etheridgii than it is in 
D. Moorei. 
Locality and stratigraphical range-—P. Etheridgii has been 
collected from the marlstone of Bredon Hill, Gloucestershire. 
Mr. Moore found it in the Upper Lias of Ilminster, and we have 
collected several specimens from the Pea-grit (Inferior Oolite) 
of Crickley and Leckhampton Hills, but have never seen a 
trace of this species in any of the upper beds ; it seems there- 
fore to have a limited vertical range betaveen the marlstone and 
the basement-beds of the Inferior Oolite, and is one of the few 
species which lived in the Liassic and Oolitic seas. 
We dedicate this species to our friend Mr. Etheridge, of the 
Bristol Museum, who has kindly assisted us in comparing our 
specimens with the fine series of Echinoderms under his care, 
and has likewise otherwise aided us in the most friendly manner 
in working out the subjects of these memoirs. 
Genus Potycyruvus, Agassiz. 
Small Urchins having a subglobular form ; the upper surface 
of the test is covered with numerous small imperforate tubercles 
of a very uniform size; the base and basal angle are furnished 
with several tubercles of a size disproportionately large when com- 
pared with those of the upper surface ; the pedal pores are dis. 
VOL. II. D 
