HUDSON-RIVER GROUP. 279 



337. 1. HETEROCRINUS HETERODACTYLUS. 



Pi.. LXXVI. Figs. 1 a - o. 



Body short, rounded, subcylindrical, tapering above and below ; pelvis composed of 

 five small pentagonal plates, wliich are succeeded by the same numljer of larger costal 

 plates, and these again by five scai)ulars ; arms irregularly subdivided ; column pentagonal, 

 composed of thick joints, which are nodulose at the angles ; joints alternating in size as 

 they approach the pelvis. 



This is a peculiar species, remarkable for the small size of the body when compared 

 with the column. The irregularity of the arrangement of the plates in the arms and 

 fingers is likewise a striking characteristic of the species, which is constant in two 

 specimens from difierent localities. In one of the arms ( fig. Id), the scapular plate ( h ) 

 supports a regular series of six or more plates (7 1 ) of similar form without division. The 

 arms at the right and left of this one are again unlike each other. Tlic one on the left has 

 three regular and gradually diminishing joints (^2) above the scapular, and of the same 

 form ; the last one supports the cuneiform joint ( |^ ), which again supports a double row 

 of joints ( or a pair of fingers ) . The arm on the right of the first mentioned, consists of a 

 pair of quadrangular joints ( 5. 3 ) , each of which supports a cuneiform joint (Li). In 

 the remaining two arms, no plates have been traced beyond tlie scapulars, and consccpiently 

 the entire form of tlie species cannot be determined. Sufficient is visible, however, to show 

 the irregular character of the arms, from which its name is given. 



Figs. 1 a, b. Two specimens of the natural size. 



Fig. 1 c. The body of the same enlarged. 1 c'. Transverse section of iho column, enlargc-d. 



Fig. 1 d. An enlarged figure, representing the structure of this species. 



Figs. 1 e,f. Fragments of slate with pentagonal columns of this species, showing the body at/'. 



The fragments of round columns in the same specimens are of another species (see 



Plate Ixxvii). 

 Fig. 1 g. A fragment of one of these columns enlarged, showing the nodulose angles. 

 Fig. 1 h. A fragment of a column, with a section of the same. 



Fig. 1 i. A fragment of slate, showing numerous impressions of the discs or plates of the column. 

 Fig. 1 k, I, m, TO, 0. The same magnified, showing the pentapttalous expansion around the canal, and 



the deeply impressed strioe, which are different in each one. Where tlic column is crystalized 



these markings are not visible. 



Position and locality. Fragments of the columns of this species are found in the shales 

 of the Hudson-river group, in nearly all localities. Of the two individuals figured, one is 

 from near Boonville in Lewis county, and the otiier from Loraine, .JeilVrson count}'; it is 

 also found near Rome, Oneida county. I have the same species from the shaly strata near 



Cincinnati, Ohio. («a/e Collection.) 



