320 SMITHSONIAN INSTITUTION 



METICHTHYOCRINUS Springer 

 Plate XXXIX 



M etichthyocrinus Springer, Jour. Geology, XIV; 1906, p. 479. — Zittel-Eastman, Textbook Paleontology, 

 1913, P- 205. 



■ ^ B . 



Fig. 42. M etichthyocrinus 



Ichthyocrinidae with rays in contact all around. Crown globose to ovoid, 

 expanding distally from radials. Infrabasals entirely within ring of basals. 

 Posterior basal not differentiated. No radianal, anal or interbrachial plates. 

 Primibrachs two. Rays widening from radials up. Arms dichotomous, inter- 

 locking, in form of mere extensions of the ray divisions. Column with proximal 

 enlargement. 



Genotype. Cyathocrinites tiaraeformis Troost. 



Distribution. Lower part of Lower Carboniferous; United States. 



M etichthyocrinus is the Carboniferous representative of Ichthyocrinus, with the radianal 

 eliminated. Along with this modification are some minor changes, such as in the shape of 

 the crown which has become relatively shorter and more rotund ; and in the bifurcation of the 

 arms, which apparently end with a large number of tertibrachs, in place of further branching 

 to small finials as in the Silurian genus. Notwithstanding the rotundity of the crown the 

 expansion begins with the radials, the rays regularly widening from the base up, and being 

 thus entirely different structurally from those of the Lecanocrinus group. With the increase 

 in convexity of the crown there is seen an occasional occurrence of small, sporadic inter- 

 brachials which break through and come to the surface (PI. XXXIX, figs, ga, b) ; these do 

 not in any way separate the rays, which close in together above them, and they appear 

 irregularly, having been seen only in a few rays of specimens of M. burlingtonensis and 

 M. clarkensis. 



The infrabasals and basals take no material part in the calyx, the former being within 

 the basal ring, and the latter mostly covered by the column. The axial canal, which is not 

 large, enters with an obtusely pentagonal section, enlarges into a small cavity within the infra- 

 basal ring, where it takes the form of a three-lobed funnel, with a little projecting lip at each 

 angle opposite the middle of an infrabasal. The inf rabasal and basal plates are considerably 



