Kliinidu-lyiil 



BRYOZOA. 



129 



RHINIDICTYA PAUPEKA Ulrich. 



PLATE V, FIGS. 19-21. 



Stictopora panpera (part.) ULRICII, 1886. Fourteenth Ann. Rep. Geol. Nat. Hist. Surv. Minn., p. 69. 



Zoarium usually less than 30 mm. high, consisting of narrow parallel-sided 

 branches, dividing dichotomously at intervals of from 4.0 to 12 mm. Near the base 

 the intervals are usually less than 6.0 mm., but further up the prevailing distance 

 between bifurcations is about 8.0 or 9.0 mm. The width of the branches is fairly 

 constant, deviating but little either way from 1.3 mm. Their thickness has not been 

 noticed to exceed 0.5 mm. Zocecia with nearly direct oblong apertures, their shapes 

 varying with age from subquadrangular to elliptical. Interspaces rather narrow, 

 or of moderate thickness. Zooecial apertures usually in ten or eleven rows, but eight 

 or nine and twelve rows often occur just after and before bifurcations. The central 

 five or six rows are arranged between raised longitudinal lines, minutely granulose 

 when perfect, while the two or three rows on each side are, besides being slightly larger 

 than usual, directed obliquely outward. Five of the central rows in 0.7 or 0.8 mm ; 

 measuring lengthwise along same eighteen or nineteen apertures in 5.0 mm. Internal 

 structure very much as in young examples of R. tnutabilis Ulrich. 



In the above diagnosis I have restricted my observations to the Minnesota form 

 occurring in the upper division of the Trenton shales at St. Paul and Cannon Falls. 

 This form should be regarded as the type of the species, and, pending further investi- 

 gations, the wisest course seems to be to restrict the use of the name to it. The 

 Kentucky and Tennessee form, occurring in the shaly upper member of the Trenton 

 group in those states, which I have referred to this species (loc. cit.), is now regarded 

 as distinct and next described as R. neglecta. I have two specimens from the "Phyl- 

 loporina beds " at St. Paul that are exceedingly like, if not identical with the latter, 

 but so far it has not been found in the shales above these beds, nor in the Galena 

 limestone division of the Trenton in Minnesota. But several examples collected 

 from the Galena shales at localities near Cannon Falls, seem to be identical with the 

 Canadian form referred to R. paupcra in 1886. A very fine example, with branches 

 spread over a space 50 mm. wide by 75 mm. long, collected at Ottawa and kindly 

 given to me by Mr. Walter R. Billings, causes me to doubt the strict propriety of that 

 reference. This specimen shows that the Canadian form agrees with typical R. pau- 

 pera in this, that the number of zocecial apertures in 5 mm., measuring lengthwise, 

 is eighteen to nineteen. Continuing our comparisons, however, we find the follow- 

 ing differences : (1) the apertures are smaller and rounder, and have a more distinct 



-9 



