14 



The thickness in the center is not more than one-eighth of 

 an inch, and at a distance of three or four inches from the 

 center is less than half an inch : cells cylindrical in the mid- 

 dle and contracted both above and below, the walls of the 

 cavities, often showing transverse striae, which appear like 

 the remains of septa. The distance of the cells from each other 

 is variable, those near the center being closer together, though, 

 in receding from the center, there are at intervals intercalated 

 rows of cells, which take the same direction, and give the cells a 

 closer arrangement towards the margin than in the interme- 

 diate space before the intercalation of the additional rows. 

 The apertures both above and below are essentially rhomboidal ; 

 but in well preserved surfaces there are remains of rays, which, 

 however, are rarely observed ;# and I have not seen them on 

 opposite sides of the same specimen. 



The various stages of decomposition, and degrees of pres- 

 ervation, present a great variety of surface aspect. In some 

 conditions, there is visible a distinct groove, extending along 

 the surface from one cell to the next, across the curving inter- 

 spaces. I have not observed in any of these specimens evi- 

 dences of the connecting stolous shown by Mr. Salter, (loc. 

 oat.) 



Geological Formation and Locality. — In the Galena limestone 

 oif Wisconsin, Northern Illinois, and the eastern part of Iowa, 

 this fossil is everywhere present, and is the most marked and 

 characteristic form in the rock. It likewise occurs sometimes 

 in positions where the Galena limestone is extremely thin, or 

 not recognized as a distinct member of the group. 



In the study of this species, which will be fully illustrated 

 in the forthcoming report, I have been furnished with speci- 

 mens by Messrs. I. A. Lapham, of Milwaukee, and J. H. Ad- 

 ams, of Lancaster ; Prof. Nason, of Beloit, Wisconsin, and 

 Mr. T. D. Robertson, of Rockford, Illinois. 



RECEPTACULITES (Selenoides) IOWENE. 



Selenoides lowensis, Owen, Report on the Geology of Wis- * 

 corfcin, Iowa and Minnesota, p. 587, pi. 2, fig. 13. 



Description. — Body discoid, convex below with a broad cen- 

 tral attachment ; tipper side depressed in the centre, with an 

 elevated and rounded border; cells arranged in radiating 

 curved lines from the centre to the preiphery, and which con- 

 tinue on the sides and lower surface ; the cells are cylindrical 



*Thia feature is very clearly set forth in a specimen f/ointhe collection of I. A. Laphara/Esq 



