160 FOSSIL CRINOIDS. 



1909), has definitely referred Marsupites, along with Uintacrinus, to the Coma- 

 tulida. 



As in Uintacrinus, the resemblance between the American and European 

 forms is very great, and they may even be of identical species. Not having 

 sufficient wealth of material with which to deduce from the average of many 

 individuals the typical form, and its limits of variation, no satisfactory proof 

 can be made. The differences pointed out are at best but very slight, indicating 

 a minimum of change for so great a geographical dispersion. 



Marsupites americanus, sp. nov. 

 PlateVI, figs. 4a, 6; 5. 



Calyx globose, wider than high; widest about middle of basals, contracting 

 toward the arm bases. Centrale larger than infrabasals. Dimensions of prin- 

 cipal specimen: — Centrale, diameter of pentagon, 18 mm.; IBB, 17 mm. high 

 by 17.5 wide; BB, 18 mm. high by 18 wide; RR, 11 mm. high by 14 wide; radial 

 facets 6 mm. wide. In a large fragment the centrale is 25 mm. wide. Radial 

 facets shallow, facing almost vertically; filling about half the distal face of 

 radial, and having a straight muscular articulation. Primibrachs 2; succeeding 

 brachials to the number of seven in the longest arm preserved wide and very 

 short, with an alternating cuneiform arrangement and an indication of syzygies 

 between Br 3 and 4; ventral groove broad and shallow. A good sized triangular 

 interbrachial plate, having straight sides and apparently joined to the brachials 

 by suture, fills the space between the arm bases. All plates very thin, and 

 covered with moderately fine radiating striae, crossing the sutures and converg- 

 ing at the centers; a strong ridge runs upward from the center of the basals, 

 two meeting at each radial facet. Further structures unknown. 



The general outline and surface ornament of this species are not different 

 from what may be seen among specimens of M. testudinarius of the English Chalk 

 from Sussex, and other places. These vary from coarse to fine striae, and with 

 such a thin, pliant calyx the contour of the fossil is largely a matter of pressure 

 in its deposition. Measurement of plates shows no substantial difference be- 

 tween the two, an average of five specimens of the English species being as 

 follows: — Centrale, 19.1 mm. wide; IBB, 19.6 mm. high by 19.5 wide; BB, 

 19.6 mm. high by 20.1 wide; RR, 12.6 mm. high by 15.7 wide; R. facets 8 mm. 

 wide. The only real difference observable in the parts preserved is that in our 

 species the brachials are shorter and wider than in M. testudhiarius; and if we 



