196 THE PALEONTOLOGY OF MINNESOTA. 



[Hclopora. 



The dismembered zoaria of this species literally made up a thin limestone 

 layer, 5 to 35 mm. thick, and about 2 meters square, which occurred in the soft 

 shales near Waynesville, Ohio. It is impossible to say how many segments may 

 have belonged to a single zoarium, but judging from their exceeding abundance 

 here it is more than probable that the number was often very large. 



Formation and locality. Rather a characteristic fossil of the upper beds of the Cincinnati group. 

 The species is known from localities in Ohio, Indiana and Illinois, and has been found at Stony Mountain, 

 Manitoba. 



Mus. Reg. No. 8113. 



HELOPORA (?) sp. nndet. 



PLATE III. FIG. 8. 



Of this form my collection contains several segments that were found associated 

 with Helopora mucronata, H. quadrala and Arthroclema armatum. After careful 

 comparisons with those species, the last especially, I am obliged to regard them as 

 probably belonging to an undescribed species, which, because of the paucity of the 

 material at hand, I thought best to leave unnamed. A small one of what I believe 

 to be the tertiary or last set of segments of A. armatum is illustrated, beside one of 

 the supposed new species, on plate III by fig. 7. This is a little shorter than usual, 

 agreeing in that respect very nearly with the form under consideration, but in the 

 greater strength of its longitudinal ridges and in the character and number of the 

 zooecial apertures in a given space, it differs from the present species, while it agrees 

 in these features with the ordinary form of the third set of segments of A. arma- 

 tum. The segments in question are shorter than the average forms of either the 

 secondary or tertiary segments of A. armatum, and taking into consideration the 

 absence of a lateral socket, which should be present in segments of this diameter, if 

 they belong to a species of Arthroclema, I think I am justified in maintaining, pro- 

 visionally, that they belong to a species of Jlelopora, with characters, briefly, as 

 follows : 



Segments short, a little over 2 mm. in length, about 0.5 mm. in diameter, cylin- 

 drical, the upper extremity truncate, the lower tapering slightly but not pointed. 

 Zooecia in from eight to ten longitudinal rows, but the more obvious arrangement is 

 in five transverse or subspiral rows. Apertui'es subovate, oblique, widely separated 

 longitudinally, closely arranged transversely, the last fact, together with the prom- 

 inence of the posterior border, giving the stems an annulated appearance. Delicate 

 ridges, which do not cross over the elevated margins of the zocccial apertures, define 

 their longitudinal arrangement. 



