4io 



SMITHSONIAN INSTITUTION 



PARICHTHYOCRINUS Springer 

 Plates LXI, LXII, LXIII 



Parichthyocrinus Springer, Amer. Geologist, XXX, 1902, p. 96; Jour. Geology, XIV, 1906, pp. 500, 519.- 

 Zittel-Eastman, Textbook Paleontology, 1913, p. 206. 



Fig. 50. Parichthyocrinus 



Taxocrinidae with rays closely abutting above interbrachiials. Crown 

 ovoid. Infrabasals prone like a columnal, but not within the ring of basals. 

 Posterior basal elongate. Radianal, if present, only in upper oblique position. 

 Right, and sometimes left, posterior radial smaller than others. Interbrachials 

 few. Primibrachs three. Arms dichotomous, interlocking. Column enlarging 

 beneath calyx. 



Genotype. Ichthyocrinus nobilis Wachsmuth and Springer. 



Distribution. Middle part of Lower Carboniferous, Burlington to 

 Keokuk; not known outside of the United States. 



With its closely abutting and interlocking arms this genus does not fit very well among 

 the Taxocrinidae, but would appear superficially to be more at home in one of the other 

 families. It might be defined as a Euryocrinus with Taxocrinoid anal side, but the latter 

 feature is so strongly marked that the genus must remain as I have placed it ; and further- 

 more, the infrabasals do not have the characteristic position within the basal ring which 

 holds Euryocrinus within its family. The infrabasals are very small, it is true, and rarely 

 seen from the exterior, but they have the form and location of a thin top columnal, as 

 shown by figure 4 of Plate LXIII ; in one species they are nearly equal in size, and the 

 small plate is usually in the anterior position. 



Still closer is the resemblance of this form to certain species of Forbesiocrinus of the 

 same stratigraphic position, having the same type of base, and in which the arms often 

 abut somewhat closely above the iBr areas. In specimens of F. zvortheni and F. multi- 

 brachiatus having a tendency toward modification of the anal side in the direction of a defi- 

 nite median series, some perplexingly close transitions may be found. Questions arising 



