234 



BULLETIISr 11, UNITED STATES NATIONAX, MUSEUM. 



As stated under the discussion of Diplotrypa, Nicholson described 

 and illustrated the minute structure of hemispheric specimens from 

 the Chasmops limestone of SAveden as Di-plotryiJa petropolitana, in the 

 belief that they were identical with Pander's Favosites petropolitanus. 

 Dybowski's conception of Pander's species, published several years 

 previously, was totally different. In fact, the two are now known to 

 belong not only to different genera but also to distinct families. 

 Since both Nicholson's Diplotrypa petropolitana and Dybowski's 

 Dianulites petropolitana are sufhciently figured and described to 



Fig. 130. — Dianulites peteopolitana. a, tangential section of the form "hexaporites," X20, 



■WITH THE usual NUMBER OF MESOPOEES; 6, SMALL PORTION OF THE SAME, X35, SHOWING GRANULES; 

 C, SEVEEAL ZOCECIA OF A TANGENTIAL SECTION, X35, IN T^^hjch CRYSTALLIZATION HAS PARTLY DESTROYED 

 THE structure; d, VERTICAL SECTION, X8, PASSING THROUGH A MACULA. GlAUCONITE LIMESTONE 

 (B2), TSWOS, ON THE WOLCHOW RiVER, GOVERNMENT OF St. PETEESBUEG. 



prevent any doubt regarding them, I have recognized this specific 

 name as a distinct species under each genus, without regard to the 

 fact that each author thought he was redefining Pander's species. 



My study of a large collection of Russian and Swedish hemispheric 

 forms, and of Dybowski's description and illustrations, has convinced 

 me that he had in mind a very common massive species with thin- 

 walled, polygonal zocecia, few mesopores, diaphragms a tube diam- 

 eter or more apart, and, finally, the wall structure of Dianulites 

 fastigiatus. The fact that he regarded Pander's Hexaporites, or, as 

 Von Leuchtenberg named it, Hexaporites fungiformis, as a variety of 

 D. petropolitana, is further evidence to me of the correctness of this 



