110 Dr. T. Wright on Fossil Echinoderms 
Affinities and differences.—Clypeaster Reidii very much resem- 
bles C. umbrella both as to height, width, and the smallness of 
its tubercles ; it is distinguished from that species by the follow- 
ing characters: C. Reidii is more elongated ; the petaloidal am- 
bulacra are longer and narrower; the mterambulacra are flat- 
tened and slightly curved; the base is quite flat, and the oral 
lobes are curved acutely inwards. In C. umbrella the interam- 
bulacra are arched and costated, the base is concave, and the 
oral lobes slope obliquely inwards. Compared with C. altus, the 
differences are found to be still greater: in C. Rezdit the test is 
broader in proportion to its length ; the petaloid ambulacra are 
narrower ; the poriferous zones are not so open at the base. The 
apical disc is convex and prominent in C. Reidii, and depressed 
in C. altus. In C. Rezdii the border is thin and sharp, and the 
base is flat. In C. altus the border is thick and rounded, and 
the base is concave. In C. Reidii the mouth is small, and the 
oral lobes curve acutely inwards; whilst in C. altus the large 
mouth lies at the bottom of a concave depression formed by the 
gradual inward sloping of the mterambulacra. The distinctions 
between our species and that of C. seutellatus and C. marginatus 
are so well defined, that it is unnecessary to make a comparison 
with them. 
Locality and stratigraphical position.-—This species is appa- 
rently from bed No. 1, the Gozo marble, but this we cannot with 
certainty state. Fine specimens are in the Jermyn Street Mu- 
seum, and in the collection of the Geological Society of London. 
We dedicate this species to his Excellency Sir William Reid, 
Governor of Malta, whose laudable efforts to form a public col- 
lection of Maltese fossils have greatly contributed to our know- 
ledge of the paleontology of the island. 
Genus Pycornyncuus, Agassiz, 1839. 
In the dismemberment of the genus Nucleolites of Lamarck, 
M. Agassiz has not been so fortunate as in other groups of 
Echinida: the characters on which, for example, Catopygus*nd 
Pygorhynchus are distinguished from Nucleolites are not satis- 
factory, as they undergo important modifications in the different 
species grouped together in each of these new genera. If we 
take a type specimen of each genus only and compare them 
together, we admit the distinctions pointed out; but when we 
examine several species of each of these genera, we observe the 
characters gradually blending into the primary type form: as 
representatives in tame, the grouping is valuable, but the zoolo- 
gical characters in our judgment are too indefinite to found 
genera thereon. With these remarks we refer provisionally the 
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