552 MISS JANE DONALD ON THE GENERA [Nov. I906, 



26. Notes on the Genera Omospira, Lophospzra, and Turritoma ; 

 xvitli Descriptions of New Proterozoic Species. By Miss 

 Jane Donald (Mrs. G. B. Longstaff). (Communicated by 

 Prof. E. J. Garwood, M.A., Sec.G.S. Bead May 9th, 1906.) 



[Plates XLIII & XLIV.] 



In my paper on some of the Proterozoic Murchisoniidee, Pleuroto- 

 mariidae, and Turritellidse, 1 1 referred to the researches of Dr. Ulrich 

 and Prof. Koken among the earlier gasteropoda, and mentioned the 

 groups into which those authors had divided them. We still require 

 much more knowledge with regard to their origin and relationship 

 before really-satisfactory divisions can be made. Unfortunately, 

 the new species that I am about to describe are not sufficiently well- 

 preserved to add much to the material previously available. None of 

 them have the apex entire, and therefore no further light is thrown on 

 the structure of the protoconch. These new species belong to three 

 genera, characterized by the possession of a band on all the whorls, 

 formed by the gradual filling-up during growth of a sinus, and not 

 a slit, in the outer lip. To two of these genera I have already 

 referred, namely, Lophospira, Whitfield, and Turritoma, Ulrich. 2 

 The other genus is Omospira, Ulrich. 3 Though Lophospira and 

 Turritoma are not really true Murchisoniidas, I have allowed them 

 to remain in that family for the present. 



Omospira, Ulrich. 



Dr. Ulrich places Omospira in the family Baphistomidae, but it is 

 not a characteristic member, for the whorls are more eonvex and 

 the spire is higher than is the case with the other genera belonging 

 to the family. He describes it thus (loc. cit.) : — 



' Shell somewhat elongate turbinate, subturriculate ; volutions seven or eight, 

 ventricose, obliquely flattened in the upper part by an obtuse shoulder-like 

 angulation ; the latter, which may or may not constitute the periphery of the 

 whorls, forms the outer margin of a wide band-like space in which the lines of 

 growth, which first curve strongly backward in their course from the suture- 

 line, are turned in the opposite direction ; a short distance before reaching the 

 angle the curve is sharpened; as in Baphistoma the junction between the two 

 curves is marked by a thin line, while beneath the outer angle the lines of 

 growth are turned somewhat gently forward. Aperture somewhat quadrate- 

 triangular, its height slightly greater than the width, narrowly rounded but 

 not effuse below ; columellar lip rather straight, not thick, usually reflexed so 

 as to hide a minute umbilical perforation. Surface-markings consisting of fine 

 lines of growth only. Type, 0. laticincta, n. sp. Ulrich.' 



Dr. Ulrich considers that Omospira was most probably derived 

 from Rapliistoma or from some unknown allied type, on account of 



1 Quart. Journ. Geol. Soc. vol. lviii (1902) p. 314. 



2 Ibid. pp. 330 & 332. 



3 Final Rep. Geol. & Nat. Hist. Surv. Minnesota, vol. iii, pt. ii (1897) 

 932. 



