THYSANOCRINID. 191 
biserial ; pinnules long. The first interbrachial large, resting upon the 
sloping upper corners of two radials and against the costals. There are two 
plates in the second range, and often smaller ones above, which connect with 
the plates of the disk. The anal side considerably wider; the first plate 
large, hexagonal, resting upon the posterior basal; the second range contain- 
ing three plates. Some species have an uninterrupted row of anal plates all 
the way to the anal opening. Interdistichals generally represented and rather 
large. Structure of the ventral disk and position of the anus only known 
in one species. (See Thysanocrinus inornatus) column round or obtusely 
pentangular. 
Distribution. — Restricted to the Niagara group of America, the Wenlock 
group of England, and its equivalent in Sweden. 
Type of the genus. — Thysanocrinus liliformis Mall. 
Remarks. — We have reduced Dimerocrinus, Glyptaster, Thysanocrinus 
and Lucrinus to one genus, finding it utterly impossible to distinguish them 
generically. There is some doubt, however, by what name the genus should 
be known. The name Dimerocrinus was applied by Phillips to two species 
from Dudley, D. decadactylus and D. icosidactylus. Both were figured but 
not described, and the figures were poor and did not reveal the character- 
istics of the genus. A meagre description was given by Miiller, who men- 
tioned “a pelvis,” succeeded by 3 X 5 radials, and two series of arm plates. 
D’Orbigny described it with three basals, succeeded by three rings of plates. 
From such vague and incorrect descriptions, Hall could not suspect that 
a species with five basals and infrabasals would be generically identical with 
species described as possessing three basals and no infrabasals, and we believe 
he was justified in proposing for his species a new genus.  Pictet and 
Dujardin and Hupé, who accepted both genera, placed them near together. 
Zittel, however, even refers them to distinct families. We were the first to 
point out the generic identity of Thysanocrinus with the forms which are 
held to represent Dimerocrinus decadactylus and D. icosidactylus, but dis- 
criminated in favor of the older name Dimerocrinus, which we now think 
was scarcely fair to Hall. Besides, we accepted Glyptaster and Hucrinus, 
though with some hesitation, making the latter a subgenus of the former. 
The name Glyptaster was proposed for a solitary specimen, described as 
G. brachiatus, in which all the plates of the calyx were obscured by matrix, 
but showing ten spreading biserial arms without visible pinnules, and it 
was principally upon the absence of pinnules, it seems, that the genus was 
? ? Oo 
