320 BULLETIN 77; UNITED STATES NATIONAL MUSEUM. 



with a similar but thinner deposit of the same tissue. Small or 

 young zooecia naturally show Httle of this thickening, but in the 

 usual examples, the dense, solid basal portion may be considered as a 

 character of value in the identification of the species. 



The internal characters seen in tangential sections have been 

 mentioned. Aside from their smaller size and the thickening noted 

 above, the zooecial tubes are quite similar to those of other Diplotrypas. 

 In vertical sections, aside from the usual, somewhat beaded walls, the 

 marked characteristic in all good species of the genus is the abundant . 

 development of diaphragms in the zooecial tubes. In the immature 

 zone these are seldom farther apart than the diameter of two tubes, 

 while in the crowded portions of the mature region, two and sometimes 

 three occur in the width of a zooecium. Altogether the diaphragms 

 are more uniformly distributed in both regions than in other species 

 of the genus. In the mesopores these partitions maintain their 

 usual distribution of about their own diameter apart. 



In size of zooecia and distribution of diaphragms, Diplotrypa 

 hicornis agrees well with the American D. limitaris, described by 

 Ulrich from the Nematopora bed of the Trenton in Minnesota. The 

 few mesopores of the Minnesota species will serve to separate the two, 

 although it is probable that D. limitaris is the American representative 

 of the common Russian form. 



Diflotrypa hicornis is an excellent species of the genus and may be 

 distinguished from associated forms by the comparatively smaU size 

 of its zooecia and the abundant development of diaphragms. D. petro- 

 politana, D. Jiennigi, and D. moniliformis have noticeably larger 

 zooecia. Difficulty may be experienced in separating certain speci- 

 mens of D. liexagonalis . Here, however, the zooecia, although quite 

 similar in size, have few diaphragms, while the mesopores are much 

 more closely tabulated. 



Occurrence. — ^Abundant in most of the divisions ranging from the 

 Glauconite limestone to the Wassalem beds. The specimens illus- 

 trated are from the Jewe limestone (Dl ) , Baron Toll's estate. Among 

 other localities are: Glauconite limestone (B2), Reval ; Echinospherites 

 limestone (Cl), at Reval, 4 miles east of Reval, and at Duboviki; 

 and in the Kuckers shale (C2), Baron Toll's estate and Erras; and in 

 the Chasmops limestone, south of Bodahamn, island of Oeland. 



Plesiotypes.—Csit. Nos. 57450 to 57458. 



British Museum, thin sections of figured type, and specimens from 

 various localities in Russia and island of Oeland. 



