SPONGES, GRAPTOLITES, CORALS. 93 
Streptelasma. ] 
This spe@ies seems to be near S. corniculum Hall, byt is readily distinguished by 
its smaller size, more rapidly expanding corallum, more distinct fovew, and less 
twisted as well as less laminar septa. S. profundwm Conrad (Hall) is straighter, has 
a deeper calyx, and is entirely without the central twisting or inosculation of the 
septa. 
Formation and locality.—Rather rare at the top of the Trenton limestone, near Fountain, Minnesota. 
Ten specimens collected by the author are now in his cabinet. 
STREPTELASMA RuSTICUM Billings. 
5 PLATE G, FIGS. 22, 23 
1851. Streptelasma corniculum EDWARDS and HAImME (non Hall). Monograph Poly. Foss. des Terr. 
Pal., pl. 7, fig. 4. 
1858. Petraia rustica BILLINGS. Geological Survey of Canada; Report of Progress for 1857, p. 168. 
1875. Streptelasma corniculum NICHOLSON (non Hall). Paleontology of Ohio, vol. ii, p. 208. 
1875. Streptelasma corniculum (partim) NICHOLSON. Paleontology of the Province of Ontario, p. 26, 
1882. Streptelasma corniculum HALL. Eleventh Report State Geologist of Indiana, p. 376, pl. 51. 
figs. 2-4. 
1889. Streptelasma rusticum MILLER. North American Geology and Paleontology, p. 205. 
1889. Streptelasma corniculum NICHOLSON. Manual of Paleontology, vol. i, p. 247, fig. 127B; p. 278, 
279, figs. 156A, B; p. 280, fig. 157; p. 297, figs. 178a, 178b. 
Original description.“ Straight or slightly curved, covered with astrong epitheca, 
which is more or less annulated with broad shallow undulations ; radiating septa 
about one hundred or usually a little more ; much confused in the center, where they 
form a vesicular mass ; every alternate septum much smaller thau the others, only 
half of the whole number reaching the center. Length from two inches and a half 
to three inches and a half. Diameter of cup one inch to one inch and a half; depth 
of cup half an inch or somewhat more.” 
This species attains a larger size than S. corniculum Hall, with which it is usually 
identified, and differs from it in having the septa more strongly twisted and coarser 
in approaching the center of the calyx, where they form a vesicular mass or pseudo- 
columella. This central twisting of the septa is not so pronounced in Minnesota 
specimens as it is in individuals from Richmond, Indiana. A large series of speci- 
mens will exhibit considerable variation in the extent of the central vesicular mass, 
and though it is usually of much coarser construction in the form described by 
Billings, it cannot be denied that the two species are very closely related. 
Formation and locality.—In the Hudson River group near Granger, and at Spring Valley, Minnesota; 
Graf, Iowa; Richmond, Indiana; Oxford and Dayton, Ohio. Snake island, lake St. John, and Manitou- 
waning, Georgian bay, Canada. 
Collectors.—W. H. Schofield, E. O. Ulrich, and the writers. 
Mus. Reg. Nos. 7753, 7754. 
