THE FAUNA OF THE ST. JOHN GEOUP. 51 



are apt to be impressed upon the other, owing to the thinness of the shell substance. The 

 change in the form of this species during growth was considerable : at first the enlarge- 

 ment was at a very slow rate ; subsequently, in the region where the most distinct septa are 

 found, the tube expanded more rapidly, and finally, in the upper half the shell, became 

 almost cylindrical, the rates of divergence of the sides being about one millimetre in a 

 length of eleven. 



Length, from the aperture to the oldest distinct septum, 23 mm., but including the 

 apical portion (detached) 35 mm. Width, 6 mm. Rate of tapering in the adult (as flat- 

 tened in the shale) about 1 to 9 for the wider two thirds of the shell, and 1 to 3J for the . 

 apical third ; the tapering of the young shell was about 1 in G mm. 



Horizon and Lornlit]/. In the fine dark shales of \.(1, at Porter's Brook, St. Martin's, 

 Frequent. 



Hyolithesi (Camerotheca) MirjiAC. (Plate VI. Figs. 3 and 3a.) 



Hyolithes Micmac, U.S. Geol. Surv., Bull. 10. 



The original description of this species is as follows : — " Form, that of an extremely 

 elongate, rounded, subtriaugular pyramid, that becomes gradually attenuated toward the 

 apex. The true trausA^erse section is not preserved, owing to the crushing down of the 

 shell, and appears to have been semi-elliptical or rounded subtriaugular. — Form of aper- 

 ture and operculum, unknown. — Surface of the shell, smooth, externally ; the interior, 

 marked by fine, raised, longitudinal lines. — In form this species is not unlike HyoUlhes 

 (Camerolheca) Danianus, but the smooth outer surface and striated inner surface distin- 

 guish it from that and also from any other described species known to me. — Dimen- 

 sions : Length of specimen, 20 mm. ; width at aperture, 4 mm. — Formation and Locality. 

 Cambrian, St. John formation, associated with Microdiscus punctaius, var. pulchellus at RatcliflPs 

 Millstream, N.B." 



New material enables me to add to the description of this species. The form of the 

 aperture differed from that of all the other species known in the St. John group, in that 

 the dorsal side was but slightly arched upward at the lip ; the aperture of the shell was 

 somewhat campanulate, the ventral side being enlarged (as in Hyolithes cinctus and H. 

 parens, Barr.) 



The surface of the shell, though appearing to be smooth when viewed from the side, 

 when viewed from the end with a lens, is seen to be crossed by numerous, fine striae, and by 

 sharp though low ridges, which are at nearly equal distances apart. With the aid of a 

 strong lens also, very fine and close longitudinal striae may be detected on the outer sur- 

 face. 



A few individuals have been found which have traces of septa near the apex, and Mr. 

 C. D. Walcott informs me that specimens in the Hartt collection also show this feature. 

 The shell of this species, like that of C. gracilis, is thin, and the narrow part is sometimes 

 found bent to the right or left. 



Length, abou.t 15 mm. (one in the Hartt collection figured by Mr. Walcott is 22 mm.) 

 Width, 3Jmm. Rate of tapering about 1 to 5. 



Horizon and Locality. In the fine dark grey shales of l.r, at Hanford Brook, St. Martin's ; 

 at Ratcliff's Stream, in Simond's, and in l.r;' at Portland. 



