72 



Orthis Livia is an exceedingly elegant species, and can usually be recognised without any 

 difficulty. It is allied to 0, Vanuxemi, (Hall), but Is a larger form, and is more coarsely 

 ribbed. 



Locality and Formation. Corniferous Limestone of Port Colborne, and Lot 6, Con. 1, 

 Wainfleet. 



85. ORTHIS VANTJXEMI (Hall). 



Orthis Vanuxemi (Hall), Tenth Report on the State Cabinet, p. 136. 

 Orthis Vanuxemi (Billings), Canadian Journal, New Series, Vol. V., p. 269, figs. 17, 

 18, 19. 



Orthis Vanuxemi (Hall), Pal. N.Y., Vol. IV. Plate VI., fig. 3. 



Shell very nearly circular, compressed and flattened ; hinge-line very short, rounded. 

 Dorsal valve gently and regularly convex ; the beak hardly prominent, not incurved ; .the 

 area narrow and linear. Ventral valve with its greatest convexity in the neighbourhood of 

 the beak, nearly flat, or commonly slightly concave towards the front; the beak small, but 

 more prominent than that of the dorsal valve, somewhat arched. Area narrow and curved, 

 about one-third wider than the area of the dorsal valve. Foramen comparatively large, wider 

 than high, triangular. Surface covered with close-set, fine, elevated striae, which increase 

 both by bifurcation and interstitial addition, and which are indistinctly cancellated by concen- 

 tric striae. About five striae in the space of a line, but more in the neighbourhood of the 

 beaks. Entire surface minutely punctate ; a few concentric, imbricating lines of growth. 



As regards the characters of the interior, " the dorsal valve shows a strong cardinal process, 

 which is continued in a prominent rounded median ridge for half the length of the shell, where 

 it sometimes divides, or gradually becomes obsolete ; there are sometimes visible low trans- 

 verse ridges, which divide the muscular impression. The crural processes are prominent, and 

 sustained below by strong oblique ridges. In the interior of young specimens, the marks of 

 the external striae are visible nearly or quite to the muscular impression ; while in older speci- 

 mens these marks extend little beyond the margin. The interior of the ventral valve is marked 

 by a large flabelliform muscular impression, which reaches from one-half to two thirds the 

 length of the shell. The central or adductor impression is sometimes simple, and sometimes 

 longitudinally divided by a slight median ridge, which is stronger below. In the older shells 

 the ovarian spaces are pustulo-e. The dental lamellae are strong and divergent, supported 

 below b} r the ridge which margins the muscular impression. Vascular impressions are rarely 

 seen extending beyond the muscular area. Under a lens, the interior surface is distinctly 

 punctate. In all well-preserved specimens the exterior shows minute tubular openings in the 

 striae ; and when the striae are much worn, these also are to be seen to be tubular, while a 

 farther wearing of the surface shows more distinctly the minute punctate character of the 

 shell." -(Hall, Pal. N.Y., vol. iv., p. 47.) 



Orthis Vanuxemi is one of the most characteristic of the Brachiopods of the Hamilton 

 Formation, and though not particularly abundant in Western Ontario, it is a very com- 

 mon species in the State of New York. It is distinguished from 0. Livia by its finer striation 

 and its more circular form. It is also a smaller species, average specimens having a width of 

 about thirteen lines, and a length of about eleven lines and a half, though examples both 

 smaller and larger than this are not uncommon. Small specimens are not at all unlike the Orthis 

 hybrida (Sowerby), of the Silurian Rocks of Europe and North America. There is, also, 

 considerable doubt as to whether the 0. leucosia and 0. Penelope of Hall, from the Hamilton 

 group of the State of New York, can be regarded as more than mere varieties of 0. Vanuxemi. 



Locality and formation. Hamilton group of Widder and Bartlett's Mills, near Arkona, 

 In the Township of Bosanquet. Also at Canandaigua and at various other localities in the 

 Hamilton Formation of the State of New York. 



Genus CHONETES (Fischer). 



Shell semi-oval or transversely oblong, with a wide straight hinge-line. External margin 

 of the area of the ventral valve furnished with a row of tubular spines. Surface radiately 

 striated, often spinose. Foramen in the ventral area distinct, but partially closed by a pweudo- 

 deltidium. Valves articulated by teeth. Dorsal valve with a cardinal process which is simple 

 at the base, but bifid or grooved at the extremity. Interior of the shell pustuloseor papillose. 



