THE STRUCTURAL FEATURES OF THE BRYOZOAN GENUS 

 HOMOTRYPA, WITH DESCRIPTIONS OF SPECIES FROM 

 THE CINCINNATIAN GROUP. 



By Ray S. Bassler, 



Of the Division of Straiigraphic Paleontology. 



In 1882" Mr. E. O. Ulrich established the genus Homotryjpa for a 

 group of species typified by H. curvata^ a common and characteristic 

 fossil of the lower Lorraine at Cincinnati, Ohio, and vicinity. In 

 that paper two species were described — the one just mentioned and 

 II. (Miqua. In subsequent papers this author added twelve species 

 and varieties. Other authors have described four species which have 

 been referred to the genus. In the course of their collecting Messrs. 

 Ulrich and Nickles and the writer have discovered a large number of 

 forms belonging to this genvis, which will eventually include not less 

 than fifty species. With so great a specific representation Ilomotryjxi 

 may well rank as the most important genus, not only of the Mmiticu- 

 liporidpe., but also of the order Trepostomata. Moreover, the genus 

 is interesting from both the geologic and biologic standpoints; geo- 

 logically, because most of the species are common fossils, usually 

 of restricted vertical distribution and thus are good horizon markers; 

 biologically, because many species exhibit remarkably well certain 

 structures which indicate the bryozoan nature of the monticuliporoids. 

 It is the purpose of this paper to point out and describe these struc- 

 tures as studied from thin sections, and to define and tabulate the 

 species found in the Cincinnatian group. 



The number of species of trepostomatous brA^ozoa is so large and 

 their external characters often so similar that it appears a hopeless 

 task to identify them without thin sections, joi it is a mistake to think 

 that thin sections are always necessary. Sections are desirable, but 

 are a necessity onh' when the internal characters of a new species are 

 being studied. The structures shown in tangential sections are often 



«Jour. Cincinnati Soc. Nat. Hist., V, 1882, p. 240. 



Proceedings U. S. National Museum, Vol. XXVI— No. 1323. 



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