BRYOZOA. 203 



Arthroclema.] 



Such a possibility may seem remote, yet its realization is rendered almost probable 

 by the recent discovery of similarly curved and pointed segments that belonged 

 unquestionably to the tertiary series of a small example of A. pulchellum. 



Formation and locality. Galena shales, near Cannon Falls, Minnesota, where it is associated with 

 many other small Bryozoa. Also in the upper shales at St. Paul, Minnesota. 



Mus. Reg. No. 8116. 



ARTHROCLEMA, sp. undet. (1). 



PLATE II, FIGS. 26 and 27. 



This species is represented in my cabinet by five segments collected from the 



i 



Trenton shales near Fountain, Minnesota. It may be distinct, but the material at 

 hand is insufficient for the foundation of a species of this genus. Figures 26 and 27 

 (plate II) represent the two offering the greatest differences shown in the lot. One 

 is incomplete, having lost the two upper cycles of zooecia. It was evidently a 

 younger segment than the other, being less coarsley marked, with the angle ridges 

 straighter and more prominent. One of these segments shows a lateral scar situated 

 near the center, but it is very faintly impressed and easily overlooked. The zooacia 

 form six rows, but one segment seems to have had only five, with rather large, 

 oblique apertures ; aside from the incomplete segment (fig. 26) the transverse arrange- 

 ment of the apertures in the others is more or less irregularly spiral ; five apertures, 

 one at the extreme top, is the usual number in the segment length. Inter-apertural 

 spaces rather irregularly grano-striate. Length of segments about 2.4 mm., diameter 

 of same 0.35 to 0.4 mm. 



The species to which these segments belong is probably a close ally of A. pul- 

 chellum Billings, on the one hand, and A. striatum on the other. These relations, 

 however, cannot be determined satisfactorily until more complete collections are 

 available. 



ARTHROCLEMA, sp. undet. (2). 



PLATE III, PIGS. 35-37. 



Of this form, which is evidently related to the preceding and to A. pulchellum 

 Billings, but, so far as I can see, not identical with either, I have over twenty-five 

 more or less imperfect segments. These vary in length h-om 1.7 to 2.3 mm., and in 

 diameter from 0.3 to 0.5 mm. In several a faint, centrally situated, lateral socket is 

 distinguishable, and in most of them the zocecial apertures, of which there are four 

 or five cycles and six longitudinal rows, are inclined to be irregular in their arrange- 

 ment. A number of specimens are preserved as casts of the interior, and in these 

 (see plate III, figs. 36 [and 37) a spiral arrangement of the zooecia commonly pre- 



