330 CRETACEOUS ECHINODERMATA, 
Oreaster obtusus. (Tab. XXI. fig. 12.) R. 4. 
The very obtuse extremities of the arms of an Oreaster distinct from any of 
the preceding. The marginal plates of this species are greatly enlarged, and 
there are no intermediate central ossicula. The superior marginals are regularly 
curved, oblong, convex, and punctate ; the inferiors are similar, but smaller. 
Two series of minute ossicles, each of which is furrowed by three grooves, border 
the avenues ; they bear small spines. 
Upper chalk, Lancing, Sussex. 
Genus GontasTER, Agassiz. 
This genus, as established by Professor Agassiz (Mém. Soc. Sc. Nat. Neuchatel, 
1835), included all those pentagonal star-fishes which have their margins bordered 
by a double series of large plates bearing spines, and the upper surface nodulose. 
The species composing it are grouped by Miller and Troschel in their ‘ System 
der Asteriden,’ under their genera Oreaster, Astrogonium and Goniodiscus. Mr. 
Gray’s genera Hippasterias, Goniaster, Pentagonaster, Tosia, Paulia, Randasia and 
Anthenea, are synonymous with Goniaster, excluding Oreaster. 
I restrict the name Goniaster to the more or less pentagonal or slightly 
stellate, depressed star-fishes, margined by a double series of large plates which 
are bordered, or in many cases covered by granules (minute spines) ; these in 
fossil specimens are most frequently rubbed away. The avenues are bordered by a 
double series of short spines; the inner series are transverse and often comb- 
like. The ambulacral plates are furrowed. In many species the superior 
lateral plates at the extremity of the arms are enlarged so as to form subsidiary 
eye-plates. Such have a definite and small number of intermediate laterals, 
usually 4, 6 or 8. They form the subgenus Goniodiscus. The species, in which 
the lateral plates are numerous and even decrease to the extremities of the some- 
what produced rays, may be arranged under the subgenus Astrogonium. The 
fossil chalk species of both genera are most nearly allied to tropical forms. 
Section I. 
Goniaster (Goniodiscus) rugatus. (Tab. XXI. fig. 2 & 2*.) RB. 2. 
Body pentagonal, with short angles and nearly straight sides. Superior in- 
termediate marginal plates four, oblong convex, gibbous, rugose in consequence 
