﻿ULRICH-BASSLER] revision of paleozoic bryozoa 2 3 



MESOTRYPA ANGULARIS new species 

 I P] \ri. VII, 7 9) 



Zoarium growing from discoid expansions, ,} or 4 mm. thick and 

 4 cm. or less in diameter, into hat-shaped forms that occasionally 

 attain a diameter of 7 cm. and a height of 3 cm. Surface smooth 

 but characterized by conspicuous maculae composed of zooecia which 

 arc often twice the diameter of the ordinary ones. Zocecia angular, 

 thin-walled. 6 in 2 mm. Acanthopores numerous, strong, studding 

 the surface and very conspicuous in thin sections. Mesopores few, 

 usually wanting at the surface and when present generally restricted 

 to the clusters. Diaphragms curved, few in the early stages, more 

 numerous in mature zones where two or three may he found in a 

 tube-diameter. Mesopores comparatively numerous in the imma- 

 ture region, but pinch out as growth continues, closely tabulated. 



The zocecia are larger and their walls thinner, the maculae more 

 conspicuous, the mesopores fewer, and the acanthopores more strik- 

 ing than in any of the other species of the genus. 



Occurrence. — Not uncommon in the shaly lower half of the Lex- 

 ington limestone of the Trenton at Frankfort. Burgin, and Cnrds- 

 ville. Kentucky; and in the Trenton at Ottawa and Peterboro, 

 Canada. 



Cat. Xos. 43,182-43,185, U. S. X. M. 



Family HETEROTRYPID^E I'lrich 

 Compared with the Monticuliporidce this family is distinguished 

 by the very general — almost total — absence of cystiphragms. < )f 

 the other families of the suborder in which the tabulation of the 

 zocecial tubes is by diaphragms only, the Ample x op orida are the 

 most likely to offer difficulties in their practical discrimination. 



Certain differences in their respective wall-structures have so far 

 proved infallible and generally readily applied criteria. In the 

 Heterotrypidce, namely, the zocecial walls have the structure specially 

 designated as amalgamated. As seen in tangential sections of well 

 preserved specimens, the wall separating adjacent zooids consists 

 ( 1 ) of a moderately wide, light-colored, transversely dotted or lined, 

 central hand, which represents the amalgamated original walls, and 

 12). bordering it on each side, a concentrically laminated, secondary 

 deposit. In the Amplexoporidce, on the other hand, the wall, though 

 similarly composed of two parts, differs decidedly in this, that the 

 usually light-colored inner band is divided by a sharply defined, 

 dark line, which represents the angular outer boundary of adjoining 



