Dec, 1920] Cystids and Blastoids 45> 



the second series, vertical striae dominate; in the two lateral quadrants, 

 horizontal striae dominate. In all cases the dominating strise are crossed 

 transversely by finer stride. 



Nothing is known of the column, although the facet for its attach- 

 ment is present. Nor is anything definitely known regarding the siimmit 

 of the theca in case of any of the specimens here under investigation. 



The central part of the figure ace ompanying the original description 

 consists of one of the hexagonal plates belonging to the second series. 

 The nodes at the four extreme comers have weathered away and 

 exposed some of the structure of the interior, but there is no evidence of 

 pores connecting with this interior. The four exterior ridges connecting 

 the central umbonal part of this plate with the nodes at its four extrem- 

 ities are well shown, but the fifth ridge, extending directly downward 

 to the basal angle of the thecal plate, is poorly indicated. From this 

 basal angle, in a complete specimen, the ridge continues downward 

 along the sutures between two of the basal plates, narrowing toward 

 the base, but this part of the specimen is not preserved in the figured 

 type, and the figure here is misleading. The group of horizontal ridges 

 dominating the plates of the second series at mid-height is not ade- 

 quately demarcated from the striae above and below this horizontally 

 ridged zone. 



6. Lycocystites nodosus (Hall). 



(Plate I, Figs. 11 A, B, C, D.) 



Echinocystites nodosus Hall, 20th Rep. New York State Cab. Nat. Hist., 1868, 

 p. 316, PL 12, Figs. 10, 11.) 



Lysocystites nodosus Miller, N. Am. Geol. Pal., 1889, p. 259 (Echinocystites 

 preoccupied) . 



Echinocystites nodosus was based on casts of the interior of the theca 

 of a species described by Hall from the Racine dolomite at Racine, 

 Wisconsin; later the generic name was changed to Lysocystites, Echino- 

 cystites being preoccupied. The type, numbered 2024, is preserved in 

 the American Museum of Natural History in New York City. This 

 type does not present clear evidence of the direction of the sutures 

 between the plates, and therefore has been found of no service in unrav- 

 elling the plate diagram of the species, nor in determining which is the 

 top or bottom of the specimen. The clew to its structure was discovered 

 by Arthur W. Slocom, who noticed that a specimen evidently identical 

 specifically with Lysocystites nodosus fomied the cast of the interior of 

 a second specimen which was a cast of the exterior of a species having 

 the same style of ornamentation as Aethocystites sculptns Miller, from the 

 top of the Laurel limestone, at St. Paul, Indiana. Since the two spec- 

 imens still were attached to each other, there was no possibility of error 

 in the conclusion that they formed parts of the same specimen. With 

 this clew as a guide it was found possible to orient several of the casts 

 of Lysocystites nodosus belonging to Walker Museum at Chicago Uni- 

 versity- The best of these (Plate I, Figs. 11 A, B, C) is numbered 21815 

 and is from the type locality, Racine, Wisconsin. This has the following 

 structure : 



