A HERPETOCRINUS FROM THE SILURIAN OF IOWA 



A. O. THOMAS 



Recently while the writer was sorting some collections which he 

 and some of his students had gathered a few years ago at Monticello, 

 he came upon a specimen of the rare crinoid Herpetocrinus. The 

 specimen was almost wholly covered by the matrix and it was re- 

 moved only after much patient cleaning. Further search among the 

 material added three short pieces of stems while a drawer of speci- 

 mens from the same locality, collected by Mr. J. V. Henley about 

 1907, contains a coiled .stem labeled, "Crinoid stem, Monticello, Iowa, 

 J. V. H." This, too, belongs to Herpetocrinus. As far as known, 

 this is the first reported occurrence of this very unique crinoid from 

 the Iowa Silurian. 



With very few exceptions the crinoids, or sea-lilies, of the Pale- 

 ozoic were stalked forms, that is, the crown, composed of the arms 

 and the body, was supported upon a stem of varying length ; its 

 lower end may or may not have been attached. In fact, some genera 

 had the power of freeing the lower end of the stem and later of re- 

 attaching it thus permitting a certain amount of migration. To the 

 latter kind, it is thought, our Herpetocrinus belonged. In this highly 

 specialized genus the crown consists of a small elongated cup, a 

 long narrow anal tube, and long attenuated simple arms. The most 

 remarkable feature is the coiled stem in whose coils the crown could 

 be completely enveloped. At times the animal straightened out its 

 coiled stem, expanded its arms, and assumed the conventional atti- 

 tude of its more stiffly-stemmed neighbors belonging to other gen- 

 era. When coiling, the arms folded into a slender bundle about the 

 anal tube, the crown bent back against the stem, and the latter rolled 

 itself up in the opposite direction into a flat spiral with the body at 

 the center much as a garter snake coils itself to conceal its head, 

 hence the name, Herpetocrinus, meaning serpent crinoid. 



The stems of crinoids are made up of a series of flat segments 

 which ordinarily are round or somewhat pentagonal in cross section. 

 The coiling habit, however, had so modified the stem of Herpeto- 

 crinus that while it is practically round in cross section near the 

 cup, distally it becomes concave on one side, the segments being 



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