468 PALAEONTOLOGY OF ILLINOIS. 



and by 6'. constricts and venustfi (Trematopora constrict a 

 and venusta Hall,) in the Lower Helderberg group. Several 

 undescribed forms are known to me, and, so far as 1 am able 

 to judge from Billings' brief description, his Helopora circe and 

 H. variopora (Anticosti group) belong here. 



DlAMESOPORA VAUPELI Ull'ich. 

 PI. XXXIX, fig. 3, 3b, and PI. XLI, fig. 4, 4c. 



Zoarium consisting of hollow branches whose diameter varies 

 from two to five mm., the average being about three mm.; 

 thickness of zoarium a mm. or less. Surface even. Axial tube 

 circular, with nearly smooth epitheca. Apertures oval, about 

 0.18 mm. in their long diameter, arranged in very regular dia- 

 gonally intersecting rows, ten in three mm. measuring diagon- 

 ally, with prominent overarching hoods which are all directed 

 toward the distal extremity. Zocecial tubes at first prostrate 

 along the axial tube, then procumbent upon the next higher 

 zooecium, then bending abruptly to proceed more or less directly 

 to the surface. Mature portion of zoarium about twice as thick 

 as the immature. Zo(Bcial walls thin in the axial region, very 

 thick in the mature zone. Lunarium, at the lower or posterior 

 end of each zooecium, of lighter colored material than the rest 

 of the wall substance. Mesopores small, developed in consider- 

 abundance in the mature region. Diaphragms wanting. 



This is a very neat and abundant species at the foot of the 

 hills about Cincinnati, O. In the absence of maculae and other 

 features it resembles some of the Upper Silurian species of the 

 genus, but more closely a small undescribed form occurring in 

 the Trenton limestone of Canada and New York. 



The specific name is given as a small compliment to my friend 

 Mr. E. H. Vaupel, who was the first to point out its pecu- 

 liarities. 



Position and locality: Cincinnati group, Cincinnati, O. 



