B&Y020A. 309 



Trematopora? primigenia.] 



and Nicholsonella and Constellaria on the other. And yet, above all, there are pecu^ 

 liarities that postpone the determination of the systematic position of the next 

 following species till we can learn something of their ancestors. In the meantime 

 they can remain under Trematopora and their doubtful affinities be indicated by the 

 usual sign. 



As regards Trematella and Orthopora, two subgeneric names proposed by Hall,* 

 the first is clearly a synonym for Batostomella, Ulrich, the second for Rkombopora, 

 Meek. Both groups are widely different from true Trematopora. 



TREMATOPORA? PRIMIGENIA Ulrich. 



PLATE XXI, FIGS. 23-40. 



Trematopora primigenia ULRicn, 1886. Fourteenth Ann. Rep. Geol. Nat. Hist. Surv. Minn., p. 97. 



Zoarium loosely bushy, consisting of small slender ramulets, dividing dichotom- 

 ously at -varying intervals; branches cylindrical or compressed, commonly about 2 

 mm. in diameter, but varying from 1.5 to 4.0 mm., arising in greater or lesser num- 

 bers 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 

 zooecia 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 apertures. With age the apertures become somewhat 

 smaller, ovate or subcircular and direct, and the peristome or rim equally elevated 

 all around, while the interspaces were widened till in some examples they are often 

 equal to twice the width of the zocecial 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 twelve or thirteen in 3 mm., but the 

 number in that distance may vary from eleven to fifteen. 



Internal characters: In vertical sections the tubes have thin walls, are not 

 entirely vertical, and without diaphragms in the axial region. Near the surface 

 they bend outward rather abruptly when one and sometimes two diaphragms were 

 in most cases thrown across each tube. At the same time an abundant series of 

 mesopores was developed. These are crossed by from two to six diaphragms, the 



Pal. N. Y., vol. vl. p. xlv, 1887. 



