JNo.1323. f^TRXrCTTlRAL FEATVItEf^ OF TTOMOTBYrA—BASSLER. 567 



diaphragms as well as cystiphragms are present in the peripheral 

 region. The Warren ** beds of the Lorraine formation show the 

 advent of a group of species in which diaphragms are seldom, if ever, 

 shown in sections either in the axial or peripheral region of the 

 zooecial tubes. 11. coiiwiunls, an abundant Ilichniond species, may 

 be considered the type of the group, and a glance over the appended 

 table of species will show that this section will include //, hissleri 

 and 11. libana from the Lorraine, and IT. daimoni^ II. communis., 

 II. noduJo.sa^ II. austinl^ II. eylmdriea, and II. rlc1imondeni<i.'< from the 

 various divisions of the Richmond. Whether the diaphragms were 

 membraneous and not capable of preservation, or whether they were 

 not developed at all, can not be determined. Associated species of 

 the genus show diaphragms well developed in either the peripheral or 

 in both regions, and this fact, would seem to indicate that their 

 absence in this group is of structural importance. A subdivision of 

 the II. eommunis group is suggested under the discussion of the 

 cystiphragm. 



The typical section of the genus, the II. ciirvata group, includes all 

 of the described species and the new forms of this paper with the 

 exception of those mentioned above. It is by far the more important 

 group, and ranges through the Mohawkian and Cincinnatian groups, 

 while the II. communis section is confined to the upper Lorraine and 

 Richmond. 



THE CYSTIPHEAGM. 



The peculiar structures which were termed cystiphragms by Ulrich 

 are well developed in Ilomotrypa and constitute a generic feature. 

 These cystiphragms, or cystoid diaphragms as formerly termed, occupy 



« The subdivisions of the Cincinnatian group recognized in this paper are those 

 published by Nickles (Jour. Cincinnati Soc. Nat. Hist., XX, 1902, pp. 49-100). For 

 convenience of reference the classification is here repeated. 



i Upper beds. 

 Kichmond . .\ Middle beds. 

 I Lower beds. 



Warren beds. 



Mount Auburn beds. 



Corryville beds. 



Bellevue beds. 



Fairmount beds. 



-Mount Hope beds, 

 r Upper beds. 



Utica \ Middle beds. 



I Lower beds. 



The Richmond strata exposed in Illinois, Wisconsin, Minnesota, and Manitoba, 

 and termed the northwestern Richmond in the appended tables, are here correlated 

 with the Upper beds of Nickles's classification. 



Cincinnatian.. 



Lorraine 



