1034 THE PALEONTOLOGY OF MINNESOTA. 



[Helicotoma planulatoldes. 



HELICOTOMA PLANULATOIDES, n.' sp. (Ulrich.) 



PLATE LXXIV, FIGS. 2830. 



Specimens of this species range in width generally between 15 and 25 mm. The form is closely 

 related to H. planulata Salter, but there are only about four whorls instead of five, and each descends 

 slightly beneath the level of the preceding. Compared further with the Canadian species, we find that 

 the umbilicus is somewhat narrower. A more striking difference, however, is the total absence of revolv- 

 ing lines. See H. tennesseensis for comparisons with that species. 



Formation and locality. Ten specimens were obtained in the vicinity of High Bridge, Kentucky, 

 where they occurred at the top of the Stones River group or base of the Black River limestone. Two 

 others, from the Black River group of middle Tennessee, occurred in a lot of fossils received from Prof. 

 Jas. M. Safford. 



Collection. E. O. Ulrich. 



HELICOTOMA TENNESSEENSIS Safford. 



PLATE LXXtV, PIGS. 20-24. 



Helicotoma tennesseensis SAFFORD, 1869, Geol. of Tenn., p. 288. (Neither defined nor illustrated.) 



This abundant shell holds about the same size and is closely allied to H. planulata and H. planu- 

 latoides. A constant peculiarity is a narrow downward slope along the suture line. Aside from this and 

 the absence of revolving lines, we fail to see any difference between the Tennessee and Canadian species. 

 The Kentucky species, however, attains a larger size with the same number of whorls. 



Formation and locality. Very abundant in the lower division ("Central limestone") of the Stones 

 River group at Murfreesboro, Tennessee. 



Collections. Prof. J. M. Safford ; E. O. Ulrich. 



HELICOTOMA SUBQUADBATA, n. sp. (Ulrich.) 



PLATE LXXIV, FIGS. 31-33. 



Although closely related to all three of the preceding species, the present form is readily distin- 

 guished by the subquadrate section of its whorls, the junction of the outer and lower sides of the whorls, 

 which are both flattened, being rather strongly angulated. The notch-carina is not much elevated, and 

 the surface of the whorl within it is perfectly flat to the suture line. 



Formation and locality. Same as the preceding. Only two specimens have been observed, and these 

 were both received from Prof. Jas. M. Safford. 



HELICOTOMA UMBILICATA, n. sp. 



PLATE LXH, FIG. 68; PLATE LXXIV, FIGS. 26-27. 



This species has been quite generally confused with H. planulata, but after seeing a number of spec- 

 imens of both forms we are prepared to assert, with much confidence, that they are not the same. It is 

 true H. umbilicata has, like the Canadian form, revolving lines on the outer side of the whorls, but these 

 ar<j never very strong and in most cases so weak that they cannot be distinguished on even good moulds 

 of the exterior. Comparing other features, it will be found that the shell of H. umbilicata is more 

 depressed, the width of the whorls being constantly somewhat greater than the hight, while in H. planu- 

 lata the two dimensions are equal. But the differences principally relied upon in distinguishing the two 

 forms are (1) that the apertural notch is much deeper and, consequently, the lines of growth more strongly 

 recurs-jd, and (2) the umbilicus is wider and shallower In our species than in the Canadian shell. In nine 

 specimens of the latter before us the umbilicus in no case exposes quite half of the width of each of the 



