240 



Cincinnati Society of Natural History. 



ticall}' attached ; it is usually very thin ; sometimes, however, the 

 center is elevated, so as to give the zoarium the form of a depressed 

 cone. The surface is often nearly smooth, but in the more typical 

 forms is raised at intervals into low and broad monticules. Cells 

 polygonal, with very thin walls, the diameter of those of the ordinary 

 size varying from y^-^th to -Jg-th of an inch. Groups of larger 

 cells, having a diameter not exceeding -gV-h of* an inch, occupy the 

 summits and slopes of the monticules, or in the smooth forms are 

 scattered over the surface at intervals of .1 inch, measuring from centre 

 to center. The surface extension of numerous spiniform tubuli, situ- 

 ated at the angles of the cells, may be observed in well preserved ex- 

 amples. 



In longitudinal sections (PI. X., fig. 46) the tubes have thin walls, 

 and are crossed by straight diaphragms, at distances apart varying 

 from one third to a full tube diameter. All the tubes have c}*stoid 

 diaphragms, which, however, are only rarely arranged in series. The 

 spiniform tubuli can alwa}*s be recognized in a section of this kind. 



In transverse sections (Plate X., fig. 4a) the tubes are polygonal, 

 and have \ery thin walls. The spiniform tubuli are numerous and 

 rather large ; the} 7 almost invariably are situated at the angles of the 

 tubes. 



The large spiniform tubuli, and the erratic disposition of the cj^stoid 

 diaphragms are characters which will distinguish M. wetherbyi from all 

 other species of the genus known tome. Named for my friend, Prof. 

 A. G. Wetherby, whose papers have added so much to our knowledge 

 of the fauna of the Trenton Group of Kentucky. 



Formation and locality : Trenton Group, in strata about in the 

 middle of the series, at High Bridge, Ky. Collected by the author. 



Homotrypa, now gen. 



External characters. — Zoarium ramose to subfrondescent ; surface 

 smooth, or with more or less prominent monticules. Cells circular, 

 ovate or polj T gonal, with moderately thin walls. At intervals there are 

 groups of larger-sized shells, which again sometimes inclose small 

 stellate maculae, consisting of much smaller, angular cells. The sur- 

 face extensions of spiniform tubuli may often be observed at the 

 angles of the cells. 



Internal characters. — In the axial portion of the branches or fronds, 

 the tubes are "immature," and may be crossed by straight diaphragms; 

 usually diaphragms are entirely wanting in this region. The tube- 



