INVERTEBRATES. 423 



the longitudinal rays; four to five lines of chalices on each 

 ray, mostly dextral ; about fifteen to twenty to each oscule, 

 with no interjacent lines of very minute pores between them ; 

 when the longitudinal rays are worn they appear minutely 

 tubular striate. Reverse long, tuberculate, anfractious, with 

 occasional small pores. 



Comparisons. — This very large and graceful species of Polypora is allied 

 somewhat, in character, to the Retepora laxa, Phillips {Polypora, McCoy; 

 Gorgonia ripisteria, (loldfuss, vii, fig. 2), but differs from it in being much 

 larger, in branching more regularly, in having no interjacent lines of pores 

 between the chalices, and in the long, ovate form of its oscules. 



Geological position and locality : Keokuk group ; Warsaw, Illinois. 



Polypora Hamiltonensis, Prout. 



PL 21, fig. 6, 6 a. 

 Polypora Hamiltonensis, Prout. MS. 



Polyzoum depressed infundibuliform, or nearly flattened ; 

 rays bifurcating rather regularly, rounded and apparently 

 smooth below ; dissepiments short, expanding at their connec- 

 tion with the rays, which they nearly or quite equal in size, 

 scarcely more impressed than the rays, with which they also 

 agree in being rounded and nearly smooth on the under, or 

 non-poriferous side. Fenestrules oval, or oval-subcircular, 

 alternately arranged. Cell pores small, arranged in oblique 

 rows varying from three to four in each oblique ' range across 

 the rays, generally about four to each longitudinal row opposite 

 each fenestrule. Entire size unknown; fenestrules usually six 

 or seven in 0.20 inch, measuring longitudinally parallel to the 

 rays; and about eight in the same space, counting them in the 

 oblique, transverse rows. 



Geological position and locality : New Buffalo, Iowa, where it is common on 

 slabs, with one or more species of Fenestella, Crinoid columns, etc. Hamilton 

 group, of the Devonian series. Also, less abundantly, in same position at 

 Rock Island, Illinois. 



