36 I.ARVIFORM CRINOIDS 



The oral plates with the exception of the posterior one are of approxi- 

 mately similar size and shape. The posterior oral however is somewhat wider 

 than the others and its upper extremity fits in between the anterior orals thus 

 separating the left and right posterior plates. The oral dome constitutes 

 about nine-elevenths of the total height of the calyx. The plates slope gently 

 outward and downward from the center of the distal surface to a position 

 about three-elevenths of the total height below the top of the calyx, at which 

 position the greatest width is attained. They are then deflected sharply down- 

 ward and slope inward to meet the basals below. The oral plates are gently 

 concave transversely and they meet along rounded ridges which stand out 

 most prominently at the angle between the upper and lateral surfaces. 



The surfaces of the plates are roughened by very hue irregularities. 



Remarks. — This species is the most abundant of the tiny silicified crinoids 

 collected in Warren County, Indiana. About forty specimens have been 

 examined and nearly all of them are comparable in size to the holotype. 

 Were specimens of this species rarer and those of Amphipsalidocrinus scis- 

 surus more abundant it would be natural to conclude that the present form 

 is simply an immature representative of the latter species. The only conspicu- 

 ous difference between these two is the presence or absence of the arms. 

 The larger species was arm-bearing and it is easy to conceive that the arms 

 were not developed until the individuals had grown to a size exceeding that 

 of the smaller form. However, the numerical disparagement is such that this 

 can not be the case and there is no doubt but that the smaller forms are 

 mature individuals of a different species. 



Occurrence. — This species was obtained from a limestone in the lower 

 part of the Pennsylvanian deposits of Warren Count}-. Indiana, near the 

 center of the N. V2 sec. 35, T. 21 X., R. 9 W. 



Genus DICHOSTREBLOCRIXVS 1 " J. M. Weller. n. gen. 

 Genotype Dichostreblocrinus scrobiculus J. M. Weller, n. sp. 



The subpyriform calyx is composed of three rings of plates which are 

 interpreted as, (1) an infrabasal disc, (2) five basals. and (3) five orals. 

 The laterally situated anal opening has been displaced to the right from the 

 posterior interradius nearly to the right posterior radius and lies in a deep 

 scallop in the upper right-hand corner of the posterior basal. The orals on 

 the other hand have been slightly displaced to the left so that they are no 

 longer exactly interradial in position. 



A number of armless crinoids of somewhat similar calyx structure are 

 known in which displacement of the orals or of the anal opening has taken 



'"tfi'xa, in two ways; ffrpeflXis, deformed or twisted. 



