[MATTHEW] STUDIES ON CAMBRIAN FAUNAS 113 



rounded ; slightly campanulate on the ventral side of the aperture ; 

 aperture slightly raised at the lateral angles ; one or more imperforate 

 septa at the apex of the shell. The dorsal side is flat, but not concave ; 

 the sides of the ventral are also somewhat flattened. The rate of tapering 

 of the tube was 1 in 5 near the apex and 1 in 7 for the rest of the tube. 



Sculpture. — This consists of a fine granulation subordinate to close 

 fine transverse striae, scarcely visible to the naked eye. These stride are 

 diversified with a few stronger growth-lines, which show that the orifice 

 of the shell was slightly depi-essed in the middle, both on the dorsal and 

 ventral sides. 



Size. — No complete example known. The width of the aperture is 

 from 6 to 7 mm. Length of the complete shell (if not decollated) esti- 

 mated at 40 mm. 



A variety of this species (PI. VI., figs. 6a and b) in place of the 

 rounded back of the ventral side shows a flattened surface, giving a 

 somewhat quadricostate aspect to the tube, but the resultant ridges are 

 less prominent than those figured by Mr. Walcott, for the specimens of 

 H. quadricostatus, obtained by him in Newfoundland, and much less than 

 those of the type of the species obtained at Attleboro', Mass.^ 



There appears to be no related species in the Swedish Cambrian. 



0. sica may be distinguished from 0. pugio by its smoother surface, 

 more triangular section and more distinct surface striae. 



Except Hyolithes excellens this species and the preceding one are the 

 most abundant fossils in the Etcheminian limestone of Smith Sound. 



Operculum (PI. YI., fig. 4e). 



We describe here an operculum which may possibly belong to this 

 species, though it is of a form more nearly corresponding to the orifice of 

 Orthotheca stiletto (see beyond) ; but we have found no example of this 

 species large enough to contain such an operculum. 



Subtriangular, rounded on the ventral side. Nucleus one-third from 

 this side, prominent but obtuse. Prom the nucleus to the ventral margin 

 all around the operculum is convex, conversely there is a triangular 

 depression extending from the nucleus and widening to the dorsal border. 



Sculpture. — The surface is finely granulated, but faint engirdling 

 striae may be detected. 



Size. — Length, 4^ mm. ; width, 3 mm. 



Orthotheca stiletto (PI. VL, figs. 3a and b). 

 Orthotheca stiletto, Nat. Hist. Soc. N.B., Bull, xviii., p. 193, pi. ii., figs. 3a and &. 

 A small, slender, straight species with a very tenuous tube. It has 



1 Mr. Walcott's species is probably an Orthotheca as the rate of tapering is 1 to 

 6§ ; Shaler and Foerste's species on the contrary tapers 1 to 2^, which indicates a 

 Hyolithes. 



Sec. IV., 1809. 8. 



