56 
SMITHSONIAN INSTITUTION 
which were considered quite wonderful, and the Troost collection which has since become 
accessible was not much better supplied. The few calices that had been picked up on the 
glades consisted mostly of the dorsal cup, or of the basal plates only, with the surface more 
or less smoothed by erosion, and such as were found were usually assumed to belong to 
Roemer’s species, M. tennesseensis. The publication later of Troost’s monograph (Bull. 64, 
U. S. Nat. Mus., 1909) indicated the existence of a wider range of forms than had been 
previously known, and brought out a number of new specific names, but the preservation of 
the specimens was for the most part poor, and not much aid was given toward fixing the 
diagnostic characters of the species. The elaborate original descriptions were of specimens 
rather than of species. 
The collection now assembled furnishes for the first time adequate material for the study 
of the American forms of the genus, which seems to have flourished profusely in the Ten- 
nessee area. Most of it was derived from the shales of the Eiicdyptocrinus zone of the Beech 
River formation. These yielded numerous specimens from the soft matrix, in exquisite preser- 
vation, admitting the most delicate preparation, by which the surface ornament, details of 
tegmen, and in many cases the arms and pinnules, were brought to light with a perfection 
never before seen in this country. The study of this collection has resulted in the recogni- 
tion of ten species belonging to this field alone, of which three are new, while five of those 
proposed by Troost are confirmed by ample evidence among tbe new material. Thus we are 
able to place the leading species upon a firm footing, and to bring out in detail the great 
diversity by which the genus is characterized upon a well defined structural plan. In other 
areas a species has been described by Weller from the Racine dolomite at Chicago, and one 
by Hall from the Ohio Silurian, as well as from the Helderbergian of New York, by which 
the range of the genus is extended into the Devonian. Of the European Silurian there is a 
fine species from England, and four from Gotland described by Angelin, some of which may 
be synonyms. These forms for the most part differ consistently from the American species. 
A notable fact is the extreme rarity of this genus in the Laurel formation of St. Paul, where 
its presence is barely indicated by a few fragments. 
No genus of fossil crinoids is more clearly defined than Marsipocriniis. The general 
form, with broadly arched tegmen, and the peculiarity by which the secundibrachs rest directly 
upon the radials and are thus, as well as by contact with the large interbrachials, incorporated 
in the cup, impart a certain physiognomy by which it is readily recognized. Typically the 
calyx is low and broad in the proportion of i to 3, or i to 2, with somewhat less difference in 
the English species. Erom others of the family it is also decisively set off by its many-plated 
tegmen and large stem-lumen. 
Within the genus there are several prominent specific characters by which the limits of 
the species are fairly well defined : 
1. Form of calyx, which may be either — a, concavo-convex or hemispheric, with radial 
facets directed below the horizontal, and tegmen exceeding dorsal cup in size : or b, bi-convex, 
with radial facets intermediate and tegmen about equaling dorsal cup ; or c, convex conical ; 
dorsal cup deep convex, tegmen low conical, constricted, narrower than cup. 
2. Basal pentagon flat or convex with raised margin, to concave with basals at bottom 
of cavity. 
3. Interbrachial plate projecting Avith corrugated arch, or smooth without projection. 
4. Tegmen either — a, sharply tubercular, or with raised, angular, diamond-shaped plates, 
and ambulacra not conspicuous ; or, b, smooth, or with rounded plates, and ambulacra well 
defined. 
5. Surface markings either — a. coarse granular; b, corrugated, with coarse wrinkles 
or tubercles; c, tubercles confluent forming more or less interrupted lines or coarse striae 
part way on plates ; d, fine striae traversing the plates ; e, entirely smooth. 
6. Number of arms, 2 to the ray as in most American species, or 4 to the ray as usual in 
the European species. 
