616 GEOLOGICAL SURVEY OF IOWA. 



Actinocrimis biturbinatus ( n. a.). 



PLATE XVI. FIG. 5 and 6 a, b, c. 



BODY depressed turbinate below, conical above : base 

 small, moderately concave. Basal plates short, rounded be- 

 low. First radial plates short, twice as wide as long. Second 

 radials small, quadrangular. Third radials pentagonal, sup- 

 porting on their upper oblique sides two supraradials, with 

 modifications corresponding to each ray. The anterior ray 

 supports two arms, without supraradials proper : each an- 

 terolateral ray has four arms with two supraradials on each 

 side, and each postero-lateral ray has three arms. First in- 

 terradial plate large, eight-, nine- or ten-sided, supporting 

 in the second range two smaller plates, and these sustaining 

 the supraradials of the antero-lateral arms. First anal plate 

 longer than the first radials : second series consisting of two 

 plates ; third series of three plates, with a small central 

 plate intercalated between the second arid third series. A 

 range of three single plates in succession succeeds the third 

 anal plate, separating more widely the arms on that side. 

 Dome composed of numerous subtuberculiferous plates, and 

 terminating above in a subcentral oblique proboscis. 



ARMS slender, composed of double rows of very short joints 

 which are furnished with large jointed tentacula. Column 

 round or obtusely pentangular, composed of alternating 

 thicker or thinner joints. Surface finely granulose. 



Fig. 5. Anterior side of an individual with base somewhat longer than usual, preserving 



the arms and a portion of the column. 

 Fig. G a. Anal side of a specimen without arms, with base of proboscis which is turned 



obliquely towards the anal side. 

 Fig. 6 b. Anterior side of same. 

 Fig. c. Basal view of same. 



Fia. 95. 

 a 



[ The error in representing the arms in the figure of the 

 plate is corrected in the accompanying diagram, which illu- 



strates the relations of the arms to the rays.] 



