American Palaeozoic Bryozoa. 



155 



two rows of angular interstitial cells. Diaphragms numerous, straight. 

 Spiniform tubuli small, not numerous. Cincinnati. 



Aspidopora, Ulrich. — Very thin free expansions, with a concentric- 

 ally and radially triated epitheca covering the lower side. Composed 

 of (according to age) from one to many unequal convex spaces. Cells 

 gradually increasing in size from the margin of each convex space to 

 near the center of same. Interstitial cells numerous. Both kinds of 

 tubes crossed by diaphragms. Spiniform tubuli present. Cincinnati. 



Heterotrypa, Nicholson (restricted). — Zoarium frondescent, rarely 

 'incrusting. Tubes prismatic. Interstitial cells developed in moderate 

 numbers, sometimes collected into maculae." Spiniform tubuli small, 

 more or less numerous. No cystoid diaphragms. Cincinnati. 



Dekayia, Edwards and Haime. — Ramose, with branches cylindrical 

 or- compressed. Interstitial cells wanting. Spiniform tubuli few but 

 veiy large. They constitute a conspicuous external feature, of the 

 zoarium. Cincinnati. 



Dekayella, Ulrich. — Ramose, branches often compressed. Inter- 

 stitial cells more or less numerous, often aggregated into irregular 

 "maculae." Spiniform tubuli of two kinds: large ones arranged as in 

 Dekayia, and a much greater number of small ones. Diaphragms in 

 both sets of tubes straight. Cincinnati. 



Petigopora, Ulrich. — Small patches adhering to foreign objects, with 

 a narrow non-poriferous band or germinating membrane along the 

 outer margin. Interstitial cells wanting. Spiniform tubuli well de- 

 veloped. Cincinnati. 



Nebidipora, ? McCoy. — Thin crusts, with slightly elevated monti- 

 cules. Cells thin-walled, prismatic, and at intervals are groups of a 

 larger size. Diaphragms straight. Interstitial cells and spiniform 

 tubuli wanting. Cincinnati and Niagara. 



Discotrypa, Ulrich. — Free and very thin circular expansions. Cells 

 very regular in their arrangement, with rhomboidal or hexagonal 

 apertures. The summits of the low and broad monticules are occu- 

 pied by larger cells than the intervening spaces. Interstitial cells and 

 spiniform tubuli entirely absent. Cincinnati. 



Spatiopora, Ulrich. — Incrusting, and forming very thin, large ex- 

 pansions, with a smooth or strongly tuberculated surface. Cells shal- 

 low, with oblong and irregular apertures. Interstitial cells sparingly 

 developed. Spiniform tubuli generally of considerable size. 



Stellipora, Hall. — Zoarium incrusting. Surface studded with 

 stellate "maculae;" from the depressed central portion of these radiate 



