458 PALEONTOLOGY OF ILLINOIS. 



phragras, since in no case have I detected the unmistakable 

 appearance of cystiphragms in tangential sections. 



D. petropolitana, the type of the genus and one or two simi- 

 lar but as yet undescribed species, seem to be very different 

 from the other species now classed under Diplotrypa. In fact I 

 regard them as more nearly related to Monotrypa and Baton- 

 toma, two genera constituting with the typical section of Diplo- 

 trypa the provisionally established family DIPLOTRYPID.E. The 

 ultimate position of these genera, however, depends largely 

 upon the results of future study and discoveries. 



DlPLOTRYPA PATELLA Ull'ich. 



PI. XXXIII, fig. 2-2c. 



Zoarium lenticular; the typical specimen is twenty-five mm. 

 across, another larger example thirty-eight mm. across ; greatest 

 thickness, at centre, from two to four mm. Surface smooth, 

 thinly hirsute from the surface projections of the acanthopores, 

 showing clusters of cells larger than the average, but not ele- 

 vated above the general level. Under surface provided with a 

 thin and somewhat concentrically wrinkled epitheca. Zooecia very 

 thin walled, about eight in two mm. Apertures circular, some- 

 times polygonal, those of the normal size about 0.18 mm., the 

 larger 0.25 mm. in diameter, arranged in diagonally intersect- 

 ing series. Usually each zooDcium is touched by four others, 

 with an acanthopore situated at or very near the point of con- 

 tact. The interspaces between the zocecia are occupied by meso- 

 pores, bounded by three or four concave sides, Mesopores more 

 numerous in the clusters of larger cells. In the zooecial tubes 

 diaphragms are moderately abundant, straight, at times curved, 

 especially in the lower part of the tubes where they frequently 

 have the appearance of cystiphragms and may actually be of 

 that nature. In the mesopores the diaphragms are closely set, 

 about three in the space of a tube diameter. 



The nearest congener of this form is possibly the D. regularis 

 Foord, from which it differs in having the mesopores larger, and 

 a much larger number of diaphragms in the tubes and other 

 less important features. 



Position and locality: Cincinnati group, Oxford, Ohio, and 

 other localities. 



