PISOCRINIDAE 
73 
that except for the difference in matrix and mode of fossilization he could not undertake to 
discriminate between some of the species from the two continents. This agrees with my own 
observations made while assembling a representative series of foreign species for comparison, 
as is shown by forms herein illustrated on plate 25. 
Bather’s studies upon the morphology of Pisocrinns were very important, especially in 
placing upon a logical basis the orientation of the calyx, which had not theretofore been 
properly understood. Thus the relation of the peculiar large plate lying underneath the right 
posterior and right anterior radials as the radianal became clear. He recognized three de- 
scribed species in the European Silurian, and noted an undescribed species from Dudley. 
In America eleven species have been described, of which at least one is a synonym. 
Certain of these species are beautifully distinct, so that there is not the least difficulty in 
recognizing them, even from inferior specimens ; such, for example, as P. gcmmiformis and 
P. baccula, occurring at the same locality in the Laurel formation, and P. quinquelobus and 
P. tennesseensis of the Brownsport ; whereas P. campana is so variable and widely distributed 
that some varieties are easily confused with other species, and one is inclined to see among 
them an admixture of European forms. 
For one of so small and inconspicuous a habitus, this genus possesses some remarkably 
distinctive characters. In the unequal distribution of radials, it partakes of the singular type 
of irregularity which characterises its family, as well as the Calceocrinidae and several other 
monocyclic genera, such as Heterocrinus, Haplocrinus, Mycocrinns, Catillocrinus, etc., in 
which two of them — and those always the same, 1. post, and ant. — are simple, larger than the 
others and of a different shape, while the other three are transversely divided or much re- 
duced in size. The projecting processes between the radial facets are peculiar to this and a 
few other genera having narrow, unbranched arms ; their varying shape offers useful specific 
characters; the projections are often built up about equally from the apposed radials, in 
which case the interradial suture bisects the process, while in others the division may be 
unequal, or the projection entirely confined to one of the radials. 
The inequality and difference in shape of the basals is a character in which this genus 
differs from most other crinoids, even from those of its own family. 
The arms are characterized b}^ a great length of brachials — an unusual feature which 
is repeated in some of the contemporaneous Calceocrinidae. This fact led S. A. Miller into 
some curious notions about the brachial appendages of Pisocrinus, he declaring with charac- 
teristic assertiveness that they were not arms, but something else of unknown function for 
which he coined a new term, “ arm blades.” The arms vary considerably in length in different 
species; in some it seems as if they were limited almost to a single brachial, while in others 
they extend to a dozen or more. The ventral furrow in some species is broad and deep, 
fringed with side pieces so large as to produce a considerable resemblance to pinnules (pi. 24, 
figs. 8, 9) . 
The structure of the tegmen, which was formerly misunderstood — certain isolated, radi- 
ately folded, conical plates being supposed to belong to it which we now know to be the fused 
orals of Gazacrinus — has been made clear by the discovery of two specimens in which it is 
perfectly preserved, consisting of five closely apposed orals similar to those of Syinbathocrinus. 
The characters available for the discrimination of species are for the most part well 
defined. They are ; 
1. General form of calyx, whether a, conical, elongate, or short and wide; b, ovoid, ex- 
panding upward or contracting ; c, globose ; d, lobed or round. In some species these 
are constant and reliable, while in others with a wide range of variation all of the first 
three may be included. 
2. Base, whether a, convex with small indented column-facet ; b, concave, broad and shal- 
low, or with deep, funnel-shaped pit ; c, truncate, with column-facet almost to full 
width. 
