no. 1611. NEW INVERTEBRATES FROM COLORADO—HENDERSON. 268 
south of Fort Collins, Colorado, the small one at the same horizon 
6 miles north of Fort Collins, two medium examples in the bluffs 
southeast of Windsor just below what is usually considered the di- 
viding line between Pierre and Fox Hills strata, and another south- 
west of Windsor at a slightly lower horizon. All but the type are 
in the University of Colorado cabinets. 
SERPULA MARKMANT, new species. 
Plate XIII, figs. 8, 9. 
Tube irregular in form, sometimes abruptly bending, perfectly 
circular in cross-section, tapering rapidly enough for the detection 
of the larger and smaller ends of specimens only 5 mm. in length. 
Outer surface of the larger specimens roughened by irregular, inter- 
rupted transverse ridges, some of the larger ones appearing to encircle 
the tube and possibly all doing so obscurely; no growth lines visible; 
inside of tube perfectly smooth, showing no traces of the ridges or 
other roughness, so that the surface of inner casts, though composed 
of fine grains of sand, are as smooth as glass; walls of the tube rather 
thin, exhibiting two layers, the inner one of much darker color than 
the outer; tubes often attached to each other for considerable dis- 
tances, but none found attached to other organic remains; length of 
largest example 45 mm., diameter at larger end 6 mm., at smaller end 
4.5 mm., while another example having the same diameter at the 
respective ends is only 30 mm. long, thus showing much more rapid 
tapering. Though fossil Serpula do not show characters of much 
specific value, this species seems to be distinct from any American 
Cretaceous species yet described, and can not be readily confused 
with any except S. plana Logan from the Benton group of Kansas, 
which it would certainly closely resemble if preserved under the 
same exact conditions. The species is common in the sandstone mem- 
ber of the Pierre Cretaceous in Fossil Ridge from 5 to 7 miles south 
of Fort Collins, Colorado, and less common at the same horizon 6 
miles north of Fort Collins, but being fragile and occurring only in 
hard concretions it is almost impossible to obtain perfect specimens. 
I have seen none which appears to show either extremity. I have 
named this in acknowledgment of the services of Mr. Harvey Mark- 
man on the expedition which brought it to light. : 
The types are in the U. S. National Museum (Cat. No. 30881) and 
many other specimens in the University of Colorado cabinets. In 
Monograph XXVII of the U. S. Geological Survey* a Serpula is 
mentioned as occurring in the lower Pierre of the Denver Basin, 
which may possibly be of this species, but it has not been described 
and I have not seen it. 
@Page 78. 
