414 PALEONTOLOGY OF ILLINOIS. 



gion; in the transition period they become more numerous; in 

 the cortical region they are close-set, a tube diameter or less 

 apart. In the outer portion of this region they are often con- 

 cave, sometimes tending to the infundibular form. Mesopores 

 more closely tabulated than the zooecial tubes. Acanthopores 

 a little more than one-third as numerous as the zooecia; when 

 not situated at the angles, generally inflecting the zooecial 

 cavity a little. 



This species approaches quite closely to H. frondosa d'Orb., 

 having a somewhat similar growth; but in that species the 

 zooecia are more angular, the walls thinner, mesopores far more 

 numerous and the acanthopores rather more abundant. 



Position and locality: Cincinnati group. A common form 

 in the upper beds at Blanchester, Ohio. It also occurs at Wil- 

 mington, 111. The H. frondosa is restricted to the lower half 

 of the Cincinnati group. 



HETEROTRYPA INFLECT A Ulrich. 



PL XXXVII, fig. 2rZd. 



Zoarium frondescent, seldom over four cm. in width, six cm. 

 in heighth, and five mm. thick; usually only about three in 

 thickness. Surface smooth or with slight elevations of cell aper- 

 tures somewhat larger than the average. Zooecial tubes bend- 

 ing abruptly into the cortical region, with walls slightly flexu- 

 ous in the axial region. Zooecia apertures circular, 0.14 to 

 0.18 mm. in diameter, with about eight in two mm. A large 

 but variable number of angular mesopores scattered among 

 the zooecia, rather more numerous in the clusters. Diaphragms 

 only one or two in each zooecial tube; numerous in the meso- 

 pores. Acanthopores present in considerable numbers, frequently 

 indenting the visceral cavity, in well preserved specimen^ very 

 conspicuous on the surface, giving it a hirsute appearance. 



This species is distinguished externally from H. frondosa 

 D'Orbigny, its nearest ally, by its much more delicate growth, 

 strictly frondescent form, monticules wanting or but little ele- 

 vated, conspicuous acanthopores and larger number of meso- 

 pores. Internally it has very few diaphragms, w r hich structures 

 are abundant in M. frondosa. 



Position and locality: Cincinnati group, Cincinnati, Ohio. 



