BRYOZOA. 373 



phragms more distant farther along in the tubes. Transverse 

 sections show that' the tubes in the axial region are of two 

 sizes, the larger ones sub-circular, the smaller set angular. This 

 is one of the most characteristic features of the genus. 



Type: C. eleg&ntula Hall. Range, Trenton to Lower Helder- 

 berg. 



ASPIDOPORA Ulrich. Very thin free expansions, with a con- 

 centrically and radially striated epitheca covering the lower side; 

 rarely parasitic. Typically composed of (according to age) 

 from one to many unequal spaces. Cells gradually increasing 

 in size from the margin of each convex space to near the center 

 of same. Mesopores numerous. Both kinds of tubes crossed 

 by diaphragms. Small acanthopores present. 



Type: A. areolata Ulr. Cincinnati group. 



CALLOPORELLA Ulrich. Free or encrusting, thin expansions. 

 Surface smooth or undulated. Zocecial tubes cylindrical, with 

 thick walls, separated by one or two rows of angular meso- 

 pores. Zooecia apertures sub-circular, arranged in regular inter- 

 secting series. Diaphragms numerous, straight. Acanthopores 

 small and few. 



Type: C. harrisi Ulrich. Cincinnati to Niagara. 



Family TREMATOPORID.E n. fam. 



Zoaria ramose, irregularly frondescent, or parasitic. Zooecial 

 tubes thin-walled and prismatic in the immature, sub-cylindri- 

 cal in the mature region. Apertures circular, oval, or petaloid, 

 with a more or less distinct peristome. Mesopores angular, 

 abundant, usually isolating the zooecia, closed at the surface ; 

 the closure with numerous perforations showing as small hollow 

 spines or granules. Acanthopores often wanting. Zooecial tubes 

 and mesopores with diaphragms. 



TREMATOPORA Hall. Zoaria ramose; branches solid, even or 

 montiferous. Zooecia with oval or sub-circular apertures, sur- 

 rounded by a more or less elevated peristome. Interspaces de- 

 pressed, sometimes exhibiting the closed mouths of the abun- 

 dant mesopores. Zooecial tubes with thin walls and few dia- 

 phragms. Mesopores irregularly angular, generally exhibiting 



