TRIASSIC ECHINODERMATA. 



Class CRINOIDEA. 



Subclass DICYCLICA. 



Order INADUNATA. 



Suborder DENDROCEINOIDEA. 



Family PENTACRINID,£. 



Genus ISOCRINUS von Meyer. 



Isocrinus smithi Clark, n. sp. 



Plate I, figures la-b. 



Determinative characters. — Column composed of small moderately thick pentagonal joints, 

 with sharp reentering angles on the large specimens. Column perforated by small canal. 



Dimensions. — Column: Diameter of joint i to 2 millimeters; length of joint } to 1 milli- 

 meter. 



Description. — The joints are generally separated and more or less weathered, being found 

 in great numbers on many leached surfaces of limestone. The largest and best-preserved speci- 

 mens are moderately thick and show sharp reentering angles. The crenulated ridges are gen- 

 erally so badly weathered that their characters are obscured, but they are broadly petaloid 

 with rather sharp angles at their outer extremities. All the Lower Triassic forms are assigned 

 to this species. Some minor differences appear among the specimens examined, however, and 

 more than one species may be represented. 



Locality — One mile west of Paris, Bear Lake County, Idaho. 



Geologic horizon. — Columbites zone, Thaynes limestone, Lower Triassic, 150 feet above 

 strata with Meekoceras fauna, but below beds containing typical Lower Triassic forms. 



Collections. — U. S. National Museum (31184); Leland Stanford Junior University. 



Isocrinus californicus Clark, n. sp. 



Plate I, figures 2a-e 



Determinative characters. — Column composed of medium-sized rather thin pentagonal joints, 

 with sharp reentering angles. The crenulated ridges are rather narrowly petaloid, and each 

 area is sharply terminated at its outer extremity. Column perforated by large canal. 



Dimensions. — Column: Diameter of joint 2 to 5 millimeters; length of joint J to 1 milli- 

 meter. 



Description. — Several specimens of isolated column joints of Isocrinus from the Upper Trias- 

 sic rocks of California, which may or may not belong to a single species, have been examined by 

 the author. Differences in the size of the joints and the sharpness of the reentering angles 

 appear, but they may be due to difference in age of the individuals represented or by the differ- 

 ent positions of the joints on the stem. In the absence of more satisfactory criteria, therefore, all 

 the Upper Triassic Pentacrini examined have been referred to this species. The majority of 

 specimens studied are not of large size, although considerably larger than I. smithi of the Lower 

 Triassic. Most of them show deep reentering angles. The crenulated ridges are obscure in 

 many specimens, but where well preserved are rather narrowly petaloid, and each area is sharply 

 terminated at its outer extremity. A large well-marked canal perforates the column. 



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