312 BULLETIN 11, UNITED STATES NATIONAL MUSEUM. 



Genus DIPLOTRYPA Nicholson. 



Diplotrypa Nicholson, Pal. Tabulate Corals, 1879, p. 292; Genus Monticulipora, 

 1881, pp. 101, 155. — Ulrich, Journ. Cincinnati Soc. Nat. Hist., vol. 5, 1882, 

 p. 153; Geol. Surv. Illinois, vol. 8, 1890, pp. 378, 457; Geol. and Nat. Hist. 

 Surv. Minnesota, vol. 3, pt. 1, 1893, p. 285; Zittel's Textbook of Paleontology 

 (Eng. ed.), 1896, p. 275.— Nickles and Bassler, Bull. 173, U. S. Geol. Surv., 

 1900, p. 36.— Bassler, Bull. 292, U. S. Geol. Surv., 1906, p. 47. 



Callopora (part) Dybowski (not Hall), Die Chaetetiden d. Ostbaltischen Silur- 

 Formation, 1877, p. 106. 



This division of the Trepostomata was instituted by Nicholson as 

 a subgenus under Monticulipora, with Pander's Favosites petropoli- 

 tanus as the type. Just which particular species of the many hemi- 

 spheric bryozoans Pander had in mind is impossible to tell without 

 an examination of his type-specimen; indeed, it is not unlikely that 

 this author himseK confused several species. Subsequently, other 

 writers described and figured presumably the same species, but in 

 almost every case their diagnoses and illustrations are insufficient 

 for the recognition of the species. The result of this frequently 

 imperfect work was that many species in Europe as well as in America 

 have been identified as Favosites or Chsetetes petropolitanus, based 

 merely upon method of growth. Indeed, there has been no name 

 so frequently cited where it is very probable that almost every 

 citation refers to a different form. 



In his Paleozoic Tabulate Corals, Nicholson described and illus- 

 trated the internal characters of hemispheric specimens from the 

 Chasmops limestone of Ostrogothia, Sweden, basing his new sub- 

 genus Diplotrypa upon these examples which he identified as Favo- 

 sites petropolitanus Pander. Two years previously Dybowski had 

 resurrected Eichwald's imperfectly defined genus Dianulites, and had 

 adequately described and illustrated certain Russian hemispheric 

 bryozoans as Dianulites petropolitanus (Pander). The internal struc- 

 ture of these two forms, identified as the same species, is totally 

 different, and the identification of Pander's species is still uncertain. 

 It happens, however, that the form identified by Nicholson as Pan- 

 der's species is very abundant throughout the Russian Middle Ordo- 

 vician, and likewise that Dybowski's Dianulites petropolitanus (Pan-* 

 der) is associated with the Swedish Diplotrypa petropolitana in the 

 latter country; moreover, they are generically distinct. The way is 

 thus open to clear this complicated mixture of species and genera by 

 recognizing Nicholson's identification as Diplotrypa petropolitana 

 Nicholson, and regarding Dybowski's conception of the species as a 

 valid form of Dianulites. 



The genus Diplotrypa comprises species with massive or discoid 

 free zoaria, composed of comparatively large zooecial tubes with thin, 

 prismatic walls. Mesopores are always present, although they vary 

 in number and size. The diaphragms are horizontal and more or 

 less abundant in both zooecia and mesopores; acanthopores wanting. 



