410 PALAEONTOLOGY OF ILLINOIS. 



clusters. When well preserved, the cells have their margins 

 beset with very small granules, which may be only surface or- 

 namentations, as no evidences of acanthopores have yet been 

 detected in tangential sections. Walls of zooecial tubes slightly 

 flexuous and crenulate, very thin in the axial region and but 

 little thickened in the peripheral region. Zooecial tubes oblique 

 throughout their course, with an unusually gradual curve from 

 their origin to the surface. Apertures seven or eight in two 

 mm. A few mesopores with diaphragms somewhat less than 

 their diameter apart are developed in the cortical region. One, 

 occasionally two, cystiphragms are developed in the zooecial 

 tubes in the transition period. 



In the case of complete specimens, the growth alone will easily 

 separate this species from similar forms. Fragments are readily 

 distinguished by the thin walls, and more than usual obliquity 

 of the cell apertures from any Lower Silurian species known to 

 me. In the brevity of the pheripheral region this species is like 

 H. dawsoni Nicholson, but the frondescent growth and pro- 

 nounced monticules of that species give it an entirely different 

 appearance. 



Position and locality: Birdseye horizon of the Trenton group, 

 High Bridge, Ky.; Calhoun Co., and near Dixon, 111. 



HOUOTRYPA GELASINOSA UMch. 

 PL XXXII, fig. 2-2d. 



Zoarium consisting of flattened branches, four mm., more or 

 less, in thickness. Surface without monticules, but marked with 

 conspicuous, elongated, parallel, dimple-like maculae, arranged 

 in transverse rows. Walls of zooecia thin, and flexuous or wavy 

 in the axial region, moderately thickened near the surface. 

 Zooecia subangular, about ten of the ordinary size in two mm., 

 those forming the borders of the maculae about one-half larger. 

 Mesopores angular, comparatively large and shallow, present 

 in the dimples only. Diaphragms occasionally present in the 

 axial region. Cystiphragms rather closely set. In the meso- 

 pores there are two or three diaphragms in the space of a tube 

 diameter. Acanthopores commonly situated in the angles of 



