74 
SMITHSONIAN INSTITUTION 
3. Basals, whether a, large, visible completely in side view, or only by points of the larger 
ones ; h, small, hidden at bottom of a deep cavity. 
4. Radial facets, whether wide or narrow, plain or dove-tailed. 
5. Processes, whether a, low and narrow, straight; h, angular, widening upward or inward; 
or c, high, spear-head shape. 
No discussion of the genus Pisocrinus would be complete without consideration of the 
Devonian forms from the Eifel described by Munster and Schultze ^ as Triacrimis, in which 
the arrangement of calyx plates is the same, except that it is said to have only three basals 
instead of five. This probably holds good for T. altus, but in T. depressns the basals vary 
from 3 to 5 ; and in my specimens those with 3 are rather more rare than those with 5. In 
other ways this species shows a considerable similarity to P. tenncsseensis. The tri-partite 
base of the Devonian genus is an evident derivative by fusion from the 5 basals of its Silurian 
ancestor, and the occasional occurrence of 4 and 5 basals a reversion to the older type. I am 
giving a series of figures of both species on plate 25, showing these facts. 
The other member of the family, Calycanthocrimts, also from the Devonian, represents 
a development of the same plan of radial arrangement from Triacrimis in the direction of 
the Catillocrinidae, by means of an increased number of arm-bearing segments. 
In the description of species of Pisocrinus the terms “ large ” and “ small ” are only 
relative, all forms of the genus being very small as compared with crinoids generally. The 
figures on the plates are mostly double size. 
Pisocrinus gemmiformis S. A. Miller 
Plate 2'^, figs. 1-8 a 
Pisocrinus gemmiformis Miller, Jour. Cin. Soc. Nat. Hist., 1879, p. 113, pi. 9, figs. 6a-c; 17th Ann. Rep. 
Indiana Dep. Geol., 1892, p. 6.36, pi. 6, figs. 10-12, 24-25 (adv. sheets, 1891, p. 26). — Foerste, Jour. 
Geol., 1903, p. 562. — Slocom, Field Columb. Mus., 2, Geol. Ser., 1908, p. 278, pi. 84, figs. 1-4. 
A small species: diameter of maximum specimen at lower third of cup 
6 mm., usually much smaller, ranging down to 2.5 mm. Calyx ovoid, truncate 
above, contracting at arm-facets; smaller specimens globose. Base broadly 
rounded, with cavity for column small, abruptly sunken. BB large, well exposed 
in side view, where the larger ones reach one third the height of calyx. Radial 
facets wide; processes low, narrow, rectangular, not widening inward. Arms 
short and heavy. Tegmen arched by 5 interlocking orals, closely bounded by 
the short first brachials. 
One of the two most characteristic species of the Laurel at St. Paul, where it occurs in 
abundance, mostly less than 4 mm. in diameter ; the habitus is small, larger specimens being 
tbe exception. The very low, narrow processes between the facets, coupled with the promi- 
nent basals, are the distinctive characters. The type of the original description in 1879 was 
said to be from the lower part of the Niagara group, in Ripley County, Indiana, and in that 
of 1891 in the 17th Indiana, the type locality was given as Osgood, and the species said to be 
“ now known from Madison and other places in the Niagara group of Indiana.” Thus it 
might have been derived from the Osgood or Laurel formations. According to Foerste 
(Jour. Geol., 1903, p. 562) it extends from the Osgood to Laurel in Tennessee. Slocom 
identifies it in the Racine of the Chicago area, but the altered condition of the dolomite speci- 
mens may prevent a close comparison. It is also' rej^orted from the Bainbridge limestone of 
1 Beitrage z. Petrefaktenk., 1839, p. 3. 
“ Echin. Eifl. Kalk., 1866, p. 106. 
