CEETACEOUS ECHINODERMATA. 41 



Class STELLEKOIDEA. 

 Subclass ASTEKOIDEA. 

 Order PHANEROZOMA. 

 Family ASTROPECTINIDvE. 



Genus ASTROPECTEN Schulze. 

 ASTROPECTEN (?) MONTANUS Douglas. 

 Plate VII, figure 6. 

 Aslropecten montanus Douglas, 1903, Carnegie Mus. Ann., vol. 2, pp. 5-8, text fig. 



Determinative characters. — Douglas says: "Size small; arras narrow and gradually tapering, 

 longer than the diameter of the body; five radial elliptical figures on body, all except one nearly 

 in line with the long axis of the arms. " 



Dimensions. — From the central pit to end of perfect arm 12 millimeters. From central 

 pit to margin of body between the arms 3.5 millimeters. 



Description. — Douglas in his description of the form says that the most prominent markings 

 are the pits which probably represent the marginal plates. It is possible, however, that these 

 may be impressions of the ambulacra. Halfway from the base to the end of the arm each row 

 of pits is nearly as wide as the middle portion of the arm. Only one arm is complete. This has 

 12 pits on each side and they are opposite. 



Locality. — South fork of Sixteenmile Creek, 23 miles north of Bozeman, Mont. 



Geologic horizon. — Colorado shale, Upper Cretaceous. 



Collection. — Carnegie Museum, Pittsburgh (601). 



Family PENTAGONASTERID^. 



Genus PENTAGONASTER Schulze. 



Pentagonaster browni Weller. 

 Plate VII, figure 7. 

 Pentagonaster browni Weller, 1905, Jour. Geology, vol. 13, pp. 257, 258, fig. 1. 



Determinative characters. — Weller says: " Stellato-pentagonal in outline. Disk large, 

 apparently flat. Interradial area broadly rounded and rays elongate for the genus, rounded at 

 the extremities. Marginal plates large, about sixteen occupying each interradial arc from tip 

 to tip of adjacent rays, the character of their ornamentation not preserved." 



Dimensions. — Major radius 24 millimeters; minor radius 11.4 millimeters. 



Description. — The specimen is apparently exposed from its dorsal side, but apart from the 

 large marginal plates all the plates of this surface have been destroyed. The impressions of the 

 ambulacral furrows of the ventral surface are exposed by the weathering away of the dorsal sur- 

 face, and appear as rounded slightly elevated ridges extending from the arm pits to the center of 

 the disk, but the characters of the ambulacra are not sufficiently well preserved to be accurately 

 determined. 



The presence of highly developed marginal plates on the specimen mark it at once as a 

 member of the order Phanerozonia, and it may be placed, without serious question, in the family 

 Pentagonasteridfe. The reference of the specimen to its proper genus is less satisfactory, but 

 it seems to. agree more closely with Pentagonaster than with any other, although the interradial 

 arcs are somewhat deeper than is usual in that genus. In the recent species P. arculatus Sladen, 1 

 however, these arcs are nearly as deep as in the fossil specimen, the proportion between the 

 minor and major radii being 1 to 1.93, against 1 to 2.08 hi the fossil specimen. 



i Challenger Reports. Zoology, vol. 30, p. 277. PI. LII, figs. 1,2. 



