88 THE PALEONTOLOGY OF MINNESOTA. 



tSt 



STREPTELASMA PBOFUNDUM (Conrad ms.) Owen. 



PLATE G, FIGS. 17-19. 



1844. CyathophyllumprofundumOwEK. Geological Exploration of Iowa, Wisconsin and Illinois, 



pi. 16. flg. 5. 



1847. Streptoplasma profunda HALL. Paleontology of New York, vol. i, p. 49. 

 1847. Streptelasma profunda HALL. Ibidem, pi. 12, flgs. 4a-4d. 

 1857. Streptelasma profunda BILLINGS. Canadian Naturalist and Geologist, vol. i, p. 123, flgs. 7, 8. 



Original description. "Obliquely turbinate, often slightly curved near the base, 

 expanding above more or less abruptly ; cell profoundly deep, extending nearly to 

 the base of the coral ; margin of the cup reflexed ; surface scarcely marked by trans- 

 verse rugae ; lamellae from 36 to 60, strong, nearly equal on the margin, but distinctly 

 alternating in length within ; no transverse dissepiments or celluliferous structure." 



Billings probably was the first to point out that the three primary septa of 

 Streptelasma are plainly indicated on the outside of the corallum from which the 

 other septa branch. He says: "The mode of growth of these corals [S. corniculum 

 and S. profundum] appears to have been as follows : At first they consisted of a mere 

 point attached to the rock, when the cup commenced to form there were only four 

 partitions or lamellae ; as it increased others were added, three of the original ones 

 continuing to grow, and the fourth being undeveloped. In good empty specimens 

 of S. profunda the three large primary lamellae are very conspicuous above the 

 others on the inside of the cup, and on the outside their position is marked by three 

 upright seams extending from the top to the bottom, and from each side of which 

 the newer lamellae may be seen branching away." 



In the Canadian specimens of this species the corallum "is very little or not at 

 all curved," and the same is true of Minnesota individuals occuring in the Trenton 

 limestone and the lower portion of the shales immediately above. In Wisconsin, 

 however, where it is quite abundant near the base of the "Upper Buff" beds in well 

 preserved specimens, the curvature is more often as great as in S. corniculum Hall. 

 The point of attachment in these is often well shown, but is generally smaller than 

 in that species. 



S. profundum can be readily separated from S. corniculum by its profoundly deep 

 visceral cavity, smaller number of distinct crenulated septa which are never twisted 

 in approaching the center and in the more sharply defined lateral fossulse and greater 

 development of the four primary septa. Billings gives the number of large and 

 small septa in adult Canadian examples as about seventy-four, and this likewise is 

 true for Minnesota specimens, while those from Wisconsin vary between 60 and 72. 

 The greater variation mentioned by Hall, "lamellae from 36 to 60," is probably due 

 to young examples, which always have a smaller number of septa than adult speci- 

 mens, 



