268 BULLETIN 11, UNITED STATES NATIONAL MUSEUM. 



generic with the genotype. Ulrich was the first to point out the 

 generic characters and to assign many of this large number of species 

 to more natural positions in the classification. 



In his later work, Ulrich has considered the genus as the Silurian 

 representative of Batostoma, and has suggested dropping the latter 

 name. The discovery of two new undoubted species of Trematopora 

 in the Middle Ordovician of Russia, in addition to the wide-spread 

 T. primigenia, and the occurrence of all three in association with 

 typical Batostoma, seems sufiicient justification for the recognition 

 of both genera. 



As indicated in the above synonymy, Dybowski misinterpreted the 

 genus entirely, all of the species referred to it by him proving to be 

 typical forms of his genus Dittopora. 



Internally the distinctly beaded mesopores, and, externally, the 

 solid zooecial interspaces and peristomes may be relied upon in dis- 

 tinguishing species of Trematopora. 



Genotype. — Trematopora tuberculosa Hall. Niagaran strata of the 

 United States and Canada. 



TREMATOPORA PRIMIGENIA Ulrich. 



Text fig. 158. 



Trematopora primigenia Ulrich, Fourteenth Ann. Rep. Geol. Nat. Hist. Surv. 



Minnesota, 1886, p. 97. 

 Trematopora? primigenia Ulrich, Geol. and Nat. Hist. Surv. Minnesota, vol. 3, 



pt. 1, 1893, p. 309, pi. 21, figs. 23-40. 



This abundant American Black River species is present among the 

 small bryozoans from the Wassalem beds at Uxnorm. Ulrich has 

 given a careful description of the Minnesota specimens which applies 

 equally well to the Russian examples, and it is therefore copied below. 



Zoarium loosely bushy, consisting of small slender ramulets, dividing dichotomously 

 at varying intervals; branches cylindrical or compressed, commonly about 2 mm. in 

 diameter, but varying from 1.5 to 4 mm., arising in greater or lesser numbers from a 

 large basal expansion that is thinly spread over some cylindrical body like a crinoid 

 column. Not infrequently the branches inosculate freely. Entire zoaria varying 

 in diameter probably between 20 and 60 mm. Superficial aspect of zocecia varying 

 with age. In young stages or examples the apertures are more or less oblique, with only 

 the posterior border elevated and the interspaces in a varying degree narrower than 

 the ajDertures. With age the apertures become somewhat smaller, ovate or subcircular 

 and direct, and the peristome or rim equally elevated all around, while the inter- 

 spaces were widened till in some examples they are often equal to twice the width 

 of the zooecial orifices. At the same time the interspaces, which as a rule exhibit no 

 sign of the really very numerous mesopores, are roughened, as are also the peristomes, 

 by the development of acanthopores. These vary greatly in size and number. The 

 arrangement of the zooecial apertures is only moderately regular, there being here 

 and there spots in which they are of larger size and more widely separated than usual. 

 An average of 12 or 13 in 3 mm., but the number in that distance may vary from 

 11 to 15. 



