248 



Cincinnati Society of Natural History. 



is sometimes clear and distinct, while at other times it is scarcely 

 detectable. The walls are occasional^' thickened at the angles of 

 junction of the tubes, giving somewhat the appearance of spiniform 

 tubuli. It is quite evident though that these nodal thickenings are 

 not of this nature. 



Longitudinal sections (Plate XI., fig. 3a) show that the tabulation 

 of the larger tubes composing the clusters observed at the surface, is 

 not different from that of the ordinary tubes, the diaphragms in all 

 the tubes being straight and usually horizontal, in the axial region 

 either wanting or remote, and in the peripheral portion of the branch, 

 closety set, and often crowded. These sections also show that true 

 interstitial tubes are entirety absent. 



In transverse sections the tubes in the axial region are subequal and 

 polygonal, with very thin walls, while around the margin, where the 

 tubes are cut longitudinally, the}' have the same appearance as in the 

 peripheral portion of a vertical section. 



This species is nearly allied to the European 31. pulchella, E. and H., 

 a Wenlock Limestone species, from which it ditiers principally in hav- 

 ing more numerous diaphragms, and the line of demarcation between 

 adjoining tubes less strongly marked. 



The species above described I regard as the t} T pe of the genus 3Iono- 

 trypella, proposed in my scheme of classification, on page 153. The 

 genus will include, besid-e M. wqualis, and the species next described 

 {31. subquadrata), 31. pulchella, E. & H. (Wenlock), Chatetes quad- 

 ratics, Rominger (Cin. Gr.), 31. briareus, Nicholson (Cin. Gr.), and 

 Chcetetes consimilis, Hall (Nia. Gr.) The Trenton Group of Kentucky 

 furnishes one new species, while the Cincinnati Group has probabl}' 

 two more. The genus in its typical forms is probably most nearly al- 

 lied to Monotrypa (as founded upon 31. undulata, Nicholson), and is 

 characterized by a ramose zoarium, made up of pol} gonal tubes, usu- 

 ally ot' one kind only, that in the axial region are thin- walled. As they 

 bend outward and approach the surface the walls are appreciably 

 thickened, and the boundary line between adjoining tubes becomes 

 more or less distinctly marked. I have studied two species which dif- 

 fer from the typical forms of the genus in one character, namely, in 

 possessing a limited number of smaller cells than the average, which 

 appear to be of the nature of iuterstitial cells. The next described 

 species, 31. subquadrata, is one of these. This species, in all other re- 

 spects, resembles 31. quadrata, so nearly that I am forced to regard 

 them at least as belonging to the same genus. The other species, 



