E. S. Cobbold — Cambrian Hyolithidcv from Hartshill. 151 



of longitudinal strife ; it is uncertain whether this species is an 

 Orthotheca or Hyolithus. 



H. (0.) JEmmonsi, Ford, 1 appears to be the nearest American 

 species ; the cross section and rate of taper are very similar, the 

 principal distinguishing feature being a shallow hollow all along 

 the dorsal side, making it slightly concave. 



Horizon and Locality. — Lower Cambrian : red sandy limestone, of 

 Woodlands Quarry, Hartshill. 



(? Sub-genus) Hyolithus 2 (Holm). 

 Hyolithus (H) alatus, sp. nov. (PI. IV, Figs. 13-15 and (?) 16.) 

 ? Hyolithus cf. obscurus, Holm, Lapworth, Proc Geol. Assoc, vol. xv, pt. ix, 

 p. 343, 1898. 



Type-specimen [34]. 3 



Diagnosis. — Shell slightly curved toward the ventral side, taper 

 about 1 in 4 (equivalent apical angle 14°); greatest length about 

 24 mm., diameter of aperture 6 mm. ; apex having the same rate of 

 taper as the remainder of the shell, often filled with calcite, but no 

 septa have been observed. Section, dorsal face gently convex 

 centrally, almost concave towards the lateral angles which form 

 rounded projections, ventral face strongly convex centrally, slightly 

 concave towards the lateral angles, ratio of axis 1 : '6. Surface, 

 resembling ground glass, but marked with strise of growth, which 

 are transverse on the ventral side, but convex forwards on the dorsal. 

 Aperture in two planes, dorsal lip projecting to a distance equal to 

 about two-thirds of the longer diameter ; ventral lip a little sinuous, 

 with a rounded notch on the centre line. 



Operculum (?) : several examples occur which are assigned with 

 little hesitation to this species. In the view of the operculum as 

 usually seen the outline is nearly circular (Fig. 16), but when the 

 plate is tilted so as to bring the dorsal margin parallel to the line of 

 sight the outline conforms very closely to the section of the shell. 

 In the circular view the nucleus is distant about four-fifths of the 

 diameter from the dorsal margin, and the sides of the conical part 

 meet at an angle of 110° to 120°; the ventral portion is strongly 

 concave and rises in front (the upper side in the figure) like an 

 upturned brim to a soft felt hat to about twice the height of the 

 nucleus. The curve joining the ventral to the dorsal margin is 

 slightly indented in correspondence with the alate lateral angles of 

 the shell. 



Comparisons with other species. — The section of H. alatus is of the 

 same character as that of Hyolithus sp. a, Groom, 4 but is not provided 

 with a "blunt keel", and the proportion between the diameters is 

 different. The species is readily recognized by its alate cross section. 



H. obscurus 5 has two impressed lines on the dorsal side close to 



1 Amer. Journ. Sci., ser. in, vol. v, p. 214, figs. 3a-e. 



2 It seems doubtful whether Eichwald's genus Hyolithus can be used, sens. 

 str., also as a sub-genus. — H. W. 



3 Numbers in square brackets are those attached to the blocks on which the 

 specimens are found. 



* Groom, op. cit., 1902, p. 116. 



5 Holm, op. cit., 1893, p. 76, pi. v, figs. 29-33. 



