NO. 1323. STE UCTURAL FEA TURES OF HOMO TR YPA—BASSLER. 581 



HOMOTRYPA DAWSONI (Nicholson). 



Plate XXV, figs. 9, 10. 



Monticulipora {Heterotrypa) dawmni Nicholson, 1881. Genus Monticulipora, 

 p. 141, pi. V, 3-3 f. 



With the exception of one feature thi.s fine species was well described 

 and figured by Nicholson. His vertical section (Plate V, fig. 3e) 

 shows complete diaphragms in the mature region, and in his descrip- 

 tion he says of that region, "a moderate number of complete hori- 

 zontal tabula3 being developed;" and again, "tabulae are in all cases 

 complete and approximatel}'^ horizontal." The normal condition of 

 the species, as seen in vertical sections, is shown in our figure 9 of 

 Plate XXV. The cystiphragms are here seen to be large and rather 

 irregularly developed or altogether absent, but in the zooecial tubes of 

 the macule a full series is usually present. Diaphragm-like struc- 

 tures occur, particularly in the outer part of the peripheral region, 

 but these are probably cystiphragms, which, extending almost across 

 the cell cavity, give in certain sections the appearance of true dia- 

 phragms. In the section, figured by Nicholson, apparently all of the 

 cystiphragms presented this appearance. An entire zoarium, with its 

 broad frond and prominent, closely set monticules, is a handsome 

 cabinet specimen. 



Oceurrenee. — A characteristic but rather uncommon fossil of the 

 Lower Richmond in Ohio and Indiana, Waynesville, Ohio, being the 

 type locality. The species has been recorded as coming also from, 

 Cincinnati. This is now known to be erroneous, the Lorraine form 

 so identified being a broad, monticulated variety of 11. (Miqua., exter- 

 nally quite similar, but internally very different. 



Cat. Nos. -il749-41T52. U.S.N.M." 



HOMOTRYPA COMMUNIS, new species. ' 

 Plate XXIII, figs. 1-1. 



Zoarium of subcylindrlcal or more commonly compressed branches 

 from 5 to 10 cm. high and 4 to 8 mm. in thickness. Surface smooth, 

 with clusters composed of larger cells and raesopores. Apertures 

 direct, polygonal, rather thick-walled, with about nine in 2 mm. 

 Acanthopores seldom seen on the surface, ))ut sections show a zoce- 

 cium to be surrounded by from four to seven. Walls thin and 

 crinkled in the axial region, much thickened in the peripheral. Dia- 

 phragms wanting in both regions. Cystiphragms few, generally 

 restricted to the region transitional to the mature condition. 



Externally this species sometimes resembles //. carvata^ but inter- 

 nally is very different. The only associated form with which it might 

 be confounded is Bythopmn weel'l (James), which often bears a super- 

 ficial resemblance. Sections show the two species to be very distinct. 



Occurrence. — A common fossil in the lower part of the Richmond 



