A PRIMITIVE TYPE OF AGELACRINITES FROM THE 



RICHMOND. 



W. H. Shideler. 



Straight rays with a rather definite trimeric arrangement 

 are found in the very young of several species of Agelacrinites 

 having normally curved rays in the adult stage, but are unknown 

 in any other adult species above the Trenton. 



A primitive species of this type having straight ambulacral 

 rays with almost parallel sides and blunted ends was found in 

 the "pebble layer" in the ba,sal Whitewater beds of the Rich- 

 mond in Adams County, Ohio, and also upon Strophomena, 

 etc., in the top of the Liberty beds in Adams County and on 

 Flat Fork, near Oregonia, Warren County, Ohio. The specific 

 name rectiradiatus is proposed because of the straight condition 

 of the rays. 



In the largest specimen, 17 mm. in diameter, the rays are 

 composed of 15 pairs of rather narrow, alternating covering 

 plates (Plate V, Fig. 30, of the following paper by Dr. S. R. 

 Williams), while a 6 mm. individual has 9 pairs (Plate V, 

 Fig. 29). No other series of covering plates was seen. 



The largest individual is from the basal Whitewater of Elk 

 Run, east of Winchester, Ohio, and is in the collection of Prof. 

 S. R. Williams. The smaller specimen is from the top of the 

 Liberty or Cherry Fork, south of Harshaville. 



Agelacrinites rectiradiatus n. sp. 

 Outer plates of peripheral ring two or three rows of small vertically 

 elongate plates. Inner plates of peripheral ring two rows of quite 

 large broad plates. Ambulacral rays (food grooves) not curved, but 

 straight and instead of tapering down evenly, the ends of the rays are 

 blunt and the sides nearly parallel. Each pair of lateral rays united 

 before reaching the center, thus giving the (primitive) trimeric arrange- 

 ment of the food grooves. This, together with the straight arms, 

 produces an unusually large posterior inter-radial space. Mouth 

 plates three, one large plate abutting the posterior inter-space, angularly 

 emarginated anteriorly. Fitting into this emargination and obviously 

 a continuation of the covering plates of the anterior arm a pair of 

 anterior peristomial plates. Anus appears to consist of a single row 

 of six angular plates. Inter-radial plates on smaller specimens much 

 smaller and seemingly more numerous than on the larger specimens. 

 Plates very distinctly and evenly pitted with larger depressions than 

 those found on the plates of A. pileus. Flooring plates very delicate, 

 probably one for each pair of cover plates. 



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