62 



BULLETIlSr 77, UNITED STATES NATIONAL MUSEUM. 



This neat, incrusting fossil is extremely abundant in America, 

 where it is known in most of the Ordovician formations, beginning 

 with the Stones River. In Russia, on the contrary, it appears to be 

 less common, although specimens have been found in divisions C2, 

 Dl, and D3. The zooecia in the specimen from the Wassalem beds 

 are larger than in the more common form of the species and agree 

 exactly with examples from the lower beds of the Black River group 

 of Minnesota and elsewhere. The other localities, however, afford 

 specimens of the more typical size, and the range in this respect is 

 therefore the same as in the American examples. 



In both the large and smaller forms the zoarium is incrusting and 

 consists of uniserially arranged, slender, club-shaped zooecia, increas- 



FlG. 8.— COKYNOTRYPA DELICATULA. SPECIMENS FIGURED BY ULRICH AS STOMATOPORA PROUTANA. 

 a, FRAGMENT OF A ZOARIUM, X9; 6 AND C, TWO GROUPS OF ZOCECIA, X 25; d, SEVERAL ZOCECIA OF UN- 

 USUAL SIZE, X25. Black River (Decorah) shales, St. Paul and Minneapolis, MiNTsrESOTA. (After 

 Ulrich.) 



ing gradually in size from the narrow proximal end to the rounded 

 anterior portion. The aperture is small, subtermmal, with a slightly 

 elevated border, and about one-third the diameter of the anterior 

 third of the zooecia. The measurements for the two forms are as 

 follows: Typical specimens have zooecia 0.04 mm. in diameter at the 

 proximal end, increasing to 0.12 to 0.15 mm. at the widest part of the 

 rounded anterior portion. The zooecia vary from 0.6 to 0.8 mm. in 

 length, and 8 to 10 occur in 5 mm. The larger form varies from 0.8 

 to 1.1 mm. in length and from 0.2 to 0.3 mm. in diameter at the ante- 

 rior portion. The stolon is of variable length, as shown in figures 

 8a and 8c. The angle of divergence in both large and small zooecia 

 is about 15°. 



Wliile Corynotrypa delicatula is closely related to several American 

 forms, there is but one Russian bryozoan near enough to require 

 detailed comparison. This is C. harberi, occurring in the Lyckholm 

 beds on the island of Dago. Comparison of figures 8 and 9 will show 



