BRYOZOA. 123 



Distribution. 1 



an imaginary axis to the surface where they bend outward abruptly, often becoming 

 free and much produced. Apertures circular, sometimes scattering, usually arranged 

 in regular transverse or subspiral series. 



Type : M. cinctosum Ulrich, Chazy (perhaps lower Birdseye) limestone of Ken- 

 tucky. 



Fuller investigations and comparisons with typical and authentic examples of 

 Entalophora and Clonopora are necessary before we may be said to be in a position to 

 decide peimanently the merits of this genus. Entalophora, as now understood by 

 Hincks and Waters, seems to me to be too comprehensive and might be, with advant- 

 age to classification, divided into at least two groups of generic rank, and it is not 

 at all improbable that Mitoclema stands upon unoccupied ground. In the mean time 

 no harm can result from the use of the name for these early paleozoic species. 



MITOCLEMA(?) MUNDULUM Ulrich. 



PLATE II. FIGS. 4-6. 



Mitoclema ? mundulum ULRICH, 1890. Jour. Gin. Soc. Nat.Hist., vol. xii, p. 177. 



Zoarium ramose, very small, the branches cylindrical, 0.5 or 0.6 mm. in diameter, 

 with faint transverse striae or wrinkles over the spaces between the zooecial apertures. 

 The latter are drawn out tube-like, about 0.15 mm. in diameter, and project strongly 

 upward and outward from the surface of the small stems. Their arrangement is in 

 rapidly ascending spiral series with four or five in 2 mm. As near as can be deter- 

 mined from the material at hand, the zocecial tubes diverge equally to all sides of 

 the branches from an imaginary axis. 



Owing to the absence of specimens suitable for slicing the internal characters of 

 this species have not been determined. The generic position is therefore somewhat 

 questionable, since it may prove to have the structure of Diploclema Ulrich (Geol. 

 Sur. 111., vol. viii, p. 368), founded upon D. trentonense Ulrich, a similar form occur- 

 ring in the Trenton limestone of New York. In Diploclema the branches are slightly 

 compressed, and the zooecial apertures somewhat constricted and less prominent.* 



Formation and locality. Associated with the preceding in the topmost beds of the Trenton shales, at 

 Cannon Falls, Minnesota. 



Mus. Reg. No. 8103. 



*In his paper on VVenlock shales Bryozoa Mr. Vine has described several similar species which he originally referred to 

 .Sjjimpora and later to Knlnluiihiira Of these .S. irtfiebirix is an unquestionable Diploclema and closely allied to our Niagara 

 //. sp'UMim I hi 11. sp. The others I have not had an opportunity of examining. 



