﻿2 2 SMITHSONIAN MISCELLANEOUS COLLECTIONS [VOL. X? 



no mesopores, the zooecia being polygonal. At deeper levels meso- 

 pores can always be detected and generally become so numerous as 

 to isolate the zooecia. The acanthopores impart a degree of beauty 

 to these sections to which no drawing can do justice. 



Diaphragms vary from one to two tube-diameters apart in the 

 axial region. As the tubes turn into the peripheral zone, cysti- 

 phragms are introduced, first a large one or two, then in a crowded 

 series with three to a tube-diameter. As usual the development of 

 cystiphragms ceases and diaphragms only are found in the more 

 superficial portions. Mesopores numerous, closely tabulated, clos- 

 ing as the surface is approached. 



This species is distinguished from all others of the genus by its 

 small zooecia, very numerous acanthopores, and closely set mon- 

 ticules. 



Occurrence. — Abundant in the Lorraine of the Central Basin of 

 Tennessee. The types are from the top of Mount Parnassus, at 

 Columbia, but Negley's hill at Nashville also furnishes specimens 

 in abundance. 



Cat. Nos. 43,178, 43,179, U. S. N. M. 



Genus Mesotrypa Ulrich 

 The species described below, being abundant, widely distributed, 

 and highly characteristic fossils of the Trenton, have proved val- 

 uable aids in making stratigraphic determinations. 



MESOTRYPA ECHINATA new species 

 (Plate VII, 4-6) 



In this species the zoarium forms irregular, flattened, or convex 

 disks, 5 or 6 mm. thick and sometimes as much as 50 mm. in diam- 

 eter. Upper surface smooth, with inconspicuous macula?. Zooecia 

 small for the genus, angular to rounded, rather thick-walled, about 

 8 in 2 mm. Mesopores rather numerous, irregular in size and shape. 

 Acanthopores large, giving the surface when well preserved a spiny 

 aspect. Diaphragm 3 to 4 in a tube-diameter in the mature zones, 

 and more than their own diameter apart in the intermediate zones. 

 Mesopores closely tabulated and in the usual manner. 



The small zooecia and large acanthopores are the striking features 

 of this species. M. infula, the type of the genus, is very similar in 

 certain respects, but its acanthopores are never so large and uni- 

 formly developed. 



Occurrence. — Not uncommon in the Trenton at Nashville, Ten- 

 nessee, and at several localities in Kentucky. 



Cat. Nos. 43,180, 43,181, U. S. X. M. 



