62 
SMITHSONIAN INSTITUTION 
Known only from the fine and perfect calyx of the type specimen in the Troost collec- 
tion, and distinguished from all other known American Silurian species by having four arms 
to the ray. as in the English and Swedish species. But it is remarkable that whereas in the 
latter the interbrachial plate is compressed by the increased number of arms so that it is elon- 
gate and pointed above, in the present species it is wide and broadly truncate above as in the 
2-armed forms, the expansion at the arm bases being accommodated by the great convexity 
of the tegmen. In fact, aside from the number of arms this species bears not the slightest 
resemblance to the European forms. That other species with 4 arms existed in the Tennessee 
area is indicated by two fragments from Wayne County, insufficient for description. 
Horizon and locality. Brownsport group, Niagaran ; Decatur County, Tennessee. 
Marsipocrinus turbinatus new species 
Plate 17, figs. 11-13 
Among all the collections from the Laurel formation at St. Paul the four 
fragmentary bases here figured are the only specimens found belonging to this 
genus. They are of a wholly different type from all the other known species, 
with their turbinate base indicating a more or less elongate calyx ; but the pen- 
tagonal form, with the rim surrounding the column-facet, and the large lumen, 
would seem to settle the generic affinities of the species. 
Horizon and locality. Laurel formation, Niagaran; St. Paul, Indiana. 
Marsipocrinus coelatus Phillips 
Plate ig, figs. 2-7 
Marsupiocrimtcs coelatus Phillips, Murchison’s Sil. .Syst., 1839, p. 672, pi. 18, fig. i. — Austin, Ann. Mag. 
Nat. Hist., 1842, p. 109. — Bather, Lankester Zool., pt. 3, p. 157, fig. 70. 
A medium sized species. Calyx convex-conical, ranging from 7 to 15 mm. 
height to 12 to 30 mm. width. Dorsal cup rather deep, broadly rounded below; 
basal pentagon nearly flat, sometimes excavate, about one third the total width. 
RR mostly horizontal in mature specimens; IBr rather large, triangular; LTBr 2 
in series, the second one axillary for a second division, followed by 2 or 3 bra- 
chials passing into the biserial arms. Arms 4 to the ray, directed vertically, 
fairly stout. iBr elongate, narrowing to an apex between the rays, almost com- 
pletely enveloped by the lower brachials and incorporated in the dorsal cup. 
Tegmen low conical or rounded, composed of numerous small plates, often 
covered by a gastropod commensally attached over the anus; ambulacra not 
prominent, but distinctly marked by small covering plates, with outer branches 
running to interbrachial pinnule openings. Surface of cup striato-corrugate, 
marked in well preserved specimens by strong ridges crossing the sutures, but 
more often obsolete. Stem stout and apparently fixed. 
An abundant and well known species of the English Silurian, here figured for com- 
parison ; it has been best illustrated heretofore by Bather in the Lankester Zoology, part 3, 
page 157, figure 70. Specifically it bears little resemblance to any American form, while it is 
a fine representative of the 20-armed type which seems to have predominated in the European 
