NO. 5 CAMBRIAN TRILOBITES 329 



the same type of cranidium may have quite a different thorax and 

 pygidium and belong to distinct genera. 



Very perfect specimens of the glabella of C. (Bonnia) parvulus 

 have very faint traces of lateral furrows close to the dorsal furrow, 

 but usually the furrows are not readily determined to be present. 

 The occipital ring rises gently at its posterior center, and a blunt, very 

 small and short spine projects backward from the edge ; the base of 

 the spine is surrounded on its sides and front by concentrically 

 arranged, sharp, irregular, fine ridges. The associated free cheek has 

 a relatively strong genal angle. 



Corynexoclius {Bonnia) parvulus is associated at locality 4k with 

 Callavia hicensis Walcott. At locality 4ii, with Micromitra, Nisusia, 

 Oholella, Hyolithes communis Billings, Callavia sp., and Olenellus 

 thompsoni Hall. For the fauna at locality 2 o, see description of 

 Corynexochus senectus, p. 319. 



Matthew names a variety angifrons from a specimen of a cranidium 

 preserved as a cast in sandstone, that is " sensibly narrower " and that 

 has scarcely a trace of glabellar furrows. The locality is unknown. 

 He suggests Vermont. The figures suggest a compressed cranidium 

 of C. (Bonnia) parvulus. 



With the poor illustration of Menocephalus salteri Devine,^ it is 

 difficult to make a close comparison between it and C. (Bonnia) par- 

 vulus Billings, but there is a most striking similarity in the cranidium 

 and pygidium of the two forms, and the description of the thoracic 

 segments of M. salteri corresponds to that of the thoracic segments of 

 Corynexochus. Both have a " broad, deep groove extending out- 

 wards to the tips, which are bent down." The lower limestones of 

 Point Levis are formed of limestone boulders in a limestone matrix, 

 and Salterella pulchella Billings, a Lower Cambrian species from 

 I'Anse au Loup, has been found there." This fact prepares us to 

 expect other Lower Cambrian fossils in some of the boulders, as is 

 the case at Bic, Trois Pistoles, and other localities along the south 

 shore of the St. Lawrence River. 



Formation and locality. — Lower Cambrian : (41k) 80 feet (21 m.) 

 above base of limestone series, or zone 2 ; Point Amour, east side of 

 Forteau Bay, and (41 i and 41m) the surface of Olenellus layer; top 

 of hill back of Mrs. Flinn's house, Forteau, Forteau Bay, north shore 

 Straits of Belle Isle, Labrador ; (20) limestone boulders in conglom- 

 erate, on shore at east entrance to harbor at Bic ; also (2r) in a cut on 



Canadian Nat. and Geol., Vol. 8, 1863, p. 210, text fig. 

 ' Bull. U. S. Geol. Survey, No. 30, 1886, p. 144, pi. 13, figs. 3. 2>a- 



