204 BULLETIN 11, UNITED STATES NATIONAL MUSEUM. 



sidered of specific importance, but the practical identity of all the 

 other characters in each is beheved to show close relationship. 



The zoarium of the variety consists of small, globular or ovoid 

 bodies, less than 5 mm. in their greatest diameter, formed by the 

 layers of zooecia incrusting some foreign object. Eight specimens 

 with this form of growth have been seen. Comparing figures 109 6 

 and 110 &, the distinctly smaller zooecia of the variety are plainly 

 evident, as is also the practical identity of the other characters. 



Occurrence. — Apparently common in the Kuckers shale (C2), 

 Baron Toll's estate, near Jewe, Esthonia. 



Cotypes.—Cait. No. 57288, U.S.N.M. 



Specimens and thin sections are in the collections of the British 

 Museum. 



Fanuly HETEROTRYPIDiE Ulrich. 



The meager development of this family in the Russian strata seems 

 upon first thought quite unusual, considering the abundant American 

 representation, but a study of the generic distribution offers an 

 explanation for this disparity. Species of Eeterotrypa are quite 

 abundant in the various Trenton and Cincinnatian formations of 

 North America, but are absent entirely from strata holding the Blacki 

 River and other Atlantic faunas. They also have not been discov^ 

 ered in European rocks. Delcayella, according to present knowledge; 

 has its origin in a Black River species, D. prsenuntia, common to 

 both continents. In later times, representatives of the genus spread 

 to other faunas so that Delcayella lost its value as a strictly Atlantic 

 type. The same is true for Stigmatella and Leptotrypa, both of which' 

 have identical Russian and American representatives in Black River 

 time. Cyphotrypa is represented in the Black River by a few species, 

 but its greatest specific development is in faunas of later age, restricted 

 so far as known, to the North American interior seas. Dekayia, 

 Petigopora, and Atactopora are known only in the faunas of late 

 Trenton and Cincinnatian time. With more research into the 

 Russian Heterotrypidae, it is of course probable that the above notes 

 will require modification, but it is beheved that the following fact will 

 remain unchanged, namely that the Baltic forms belong to the generic 

 types identical with those highly characteristic of the American 

 Black River and other North Atlantic faunas. 



The Heterotrypidse are amalgamate Trepostomata differing from 

 the MonticuHporidse in having straight diaphragms instead of the 

 curved cystiphragms. Clearly defined, frequently large, typical 

 acanthopores are developed in every member of the family. Although 

 the walls of adjoining zooecia are fused, this double wall persists as a 

 distinct but thin unit which has a clean-cut individuahty, as shown 

 in sections. The other two families of the Amalgamata differ from 



