ACTINOCEINIDiE. 569 



generally but one between the other plates ; none, however, above the sec- 

 ond costals and second interbrachials. The ridges passing up the costals are 

 most prominent, and the plates themselves longitudinally angular, their sides 

 being almost even with the flattened interbrachial areas, which gives to this 

 part of the calyx a peculiarly angular aspect. 



Basals large, forming a deep cup expanding at both ends, the plates hav- 

 ing a projecting rim or transverse ridges aroitnd their lower margins, which, 

 being truncated toward the sutures, give to the lower face of the cup a tri- 

 lobate outline. Eadials large in proportion to the plates above. First cos- 

 tals less than half the size of the radials ; the second one third shorter than 

 the first, and directed obliquely outward. Distichals all axillary, quite small, 

 angular on the exterior, their lateral ends bending inward. They support an 

 arm at one side, and three palmars at the other, above which there are four 

 more bifurcations, all taking place from the third plate respectively, giving 

 off an arm to one side, which alternates with the arm of the preceding order, 

 except the upper series, which supports two arms. The main arms, as well 

 as their lateral branches, are quite delicate, the former nniserial to the fifth 

 bifurcation, the latter biserial from their origin. Regular interbrachials : 1, 

 2, 4, followed by a few smaller plates, which are on a level with the arm 

 bases, and rest against the orals. Anal plate considerably smaller than the 

 radials, and supporting two plates in the first row, three in the second, and 

 five or six in the third. Interdistichals unrepresented. Tegmen depressed- 

 convex, with a strong anal tube rising abruptly from the summit ; the plates 

 tuberculous. Orals larger than the interambnlacrals, and separated from 

 each other by the ambulacra! plates, which are large, and pass out between 

 them in two well defined alternate series, diminishing toward the arms, and 

 branching outward. Column of moderate size ; the nodal joints somewhat 

 thickest, and rounded upon the edges. 



Horizon and Locality. — Upper part of Upper Burlington limestone ; 

 Biu'lington, Iowa, and Pleasant Grove, Iowa. 



Types in the collection of Wachsmuth and Springer. 



EcTnarks. — This species in its arm structure approaches the genus 8te- 

 ganocriniis, and is also interesting for its regularly arranged, large covering 

 pieces, which pass out between the ambulacra. It is named in honor of Dr. 

 Horace G. Griffith, of Burlington, who, with a liberality for which we have 

 been often indebted to him, presented us one of the type specimens. 



72 



