Streptelasma.] 



SPONGES, GRAPTOLITES, COEALS. 



89 



Formation and locality. Abundant as natural casts of the visceral cavity near the top of the Tren- 

 ton limestone at Minneapolis, St. Paul and Cannon Falls, Minnesota. In the Trenton shales it is com- 

 mon at Minneapolis, St. Paul, Cannon Falls, Fountain, near Caledonia, and Preston, Minnesota; Decorah, 

 Iowa. Very common near the base of the " Upper BufE " beds of the Trenton in siliceous specimens at 

 Mineral Point, Beloit and Janesville, Wisconsin ; and as natural casts at Rockton, Illinois. In the Tren- 

 ton limestone at Dixon, Illinois ; " Glade limestone" of Tennessee. In the Birdseye limestone at Manheim 

 and East-Canada creek, NewYork; Canada ; and in Mercer county, Kentucky. In the Black River group 

 at Watertown and Chazy, New York ; Isle la Motte ; and Canada 



Collectors W. H. Scofleld, H. V. Winchell, C. L. Herrick, E. O. Ulrich and the writers. 



Mus. Beg. Nos. 433, 664, 710, 3487-3489, 403, 4057, 5053, 5079 V 5305, 6751, 6774, 6781, 6808, 7737-7743, 7912, 7986. 



STREPTELASMA (?) PARASITICUM, n. sp. (Ulrich). 



FIG. 6. 



Fig. 6. Streptelasma ? parasiticum Ulrich, Trenton shales, St. Paul, Minnesota, a, View of the type 

 specimen of this species, natural size ; b, several of the corallites on the opposite side of the speci- 

 men, x3 ; c, sectional view of one of the corallites, to show depth of calyx. 



Corallum small, parasitically attached to bryozoa, consisting of a variable num- 

 ber of conical cups growing in series one from the other in a manner suggesting 

 Aulopora; each about 3.5 mm. long, and 2 mm. wide across the open calyx. The 

 specimen which I regard as the type of the species, consists of ten corallites that 

 have grown in a spiral manner over the two sides and one end of a fragment of. 

 Rhinidictya mutabilis Ulrich, about 12mm. long. Of these the largest has a diameter 

 of 3 mm., and the smallest only 1.5 mm. Where there is sufficient room for their 

 unimpeded development the calices are circular and quite oblique, but at the upper 

 end of the specimen, where they are more crowded, they are nearly direct and of 

 shapes depending upon the degree in which they impinge upon each other. Outer 

 surface marked with more or less distinct vertical ribs and fine but sharp encircling 

 striae. Calices very deep, the corallites seeming to consist in great part of a mere 

 shell, exhibiting on the inner side from thirty to thirty-six, faintly denticulate, 

 septal ridges. One half of the number are exceedingly delicate and might be over- 

 looked. 



I found it impossible to remove all the matrix from the calices, so I cannot say 

 positively how the septa unite at the bottom. Fig. 36 shows all that could be made 

 'out. 



The generic position of this fossil is rather doubtful, yet it seems to me within 

 the possibilities that it may be proven to be merely the young of some species of 

 Streptelasma like the associated S. profundum. Still, the probability of such a finding 



