134 



BULLETIN 11, UNITED STATES NATIONAL MUSEUM. 



58 a, but figure 58 h in all probability refers to a species of RJiini- 

 dictya not uncommon in the Wesenberg limestone, for which I shall 

 adopt the name RJiinidictya exserta. 



The zoarium of R. exserta is of narrow, parallel-edged branches, 

 2 J to 3 mm. in width, dividing dichotomously at intervals of 15 mm. 

 or more. Zooecia with oblique to nearly direct oblong apertures, five 

 to six in 2 mm., measuring longitudinally, and 11 in the same distance 

 counting transversely. As often noted in this genus, the marginal 

 rows of apertures are usually a little larger than the average and are 

 directed outward. In young examples the zooecial interspaces are 

 thin and without surface ornament; with age they tliicken slightly 

 and exliibit rows of small granules. The latter appear clearly in 

 tangential sections, as indicated in figure 57 c. 



The internal structure of this species is very similar to that of R. 



mutdbilis, which has been so 

 fully described by Ulrich that 

 there is no necessity for repe- 

 tition. The median tubuli 

 are seen best in transverse 

 sections and are not shown 

 in the accompanying illus- 

 trations. The surface char- 

 acters of the species, although 

 fairly v/ell shown in Eich- 

 wald's figure 58 6, are per- 

 haps better illustrated in 

 Ulrich's view of R. mutabilis in. figures 56 c and d. In spite of this 

 similarity, there need be no difficulty in distinguishing R. exserta 

 because its zooecia are one-fourth to one- third agaia as large as those 

 of R. mutahilis. 



The bifoliate, narrow, straight edged parallel branches of R. 

 exserta, with its oblong zooecia, are so distinct from associated bryo- 

 zoans that there is little Hkelihood of confusing it with any other. 

 In contrast with other bryozoans of the Wesenberg limestone, all of 

 the specimens of the present species that I have seen have weathered 

 out with a distinct white color, a fact which also aids in their identi- 

 fication. 



Occurrence. — Apparently common in the Wesenberg limestone (E) 

 at Wesenberg, Esthonia; rare in the Kegel limestone (D2) at Kegel, 

 Esthonia. 



Plesiotypes.--C&t. No. 57228, U.S.N.M. 



British Museum, one specimen from the Wesenberg limestone at 

 Wesenberg. 



i 



Fig. 58. — EHINtDIC.TYA EXSERTA. a, EICHWALD'S OEIGI- 

 NAL VIEW OF THIS SPECIES; 6, VIEW OF HIS SECOND 

 SPECniEN, UPON WHICH THE PEESENT CONCEPTION OF 

 THE SPECIES IS BASED. 



