Fossils of the Chazy Limestone* 433 



LlNGULA HURONENSIS* (N. S.) 



Fig. 9. 



Fig. 9. — Lingula Huronensis. a, ventral valve ; b, dorsal aspect, 

 shewing the area of the ventral valve ; c, transverse section ; d, 

 longitudinal section. 



Description. — Sub-pentagonal, moderately convex, with three 

 flat plane sloping faces as in L. Lyellu Length nine lines, width 

 six lines, dorsal valve half a line shorter than the ventral. 



The beak of the ventral valve is obtusely pointed and the two 

 posterior or upper margins diverge from it at an angle of about 70° 

 and are straight or gently convex for a little more than one third 

 the length of the shell, then turning an obtuse angle merge into 

 the two lower lateral margins which are sub-parallel to the 

 rounded front angles; anterior margin nearly straight. 



Sarface with concentric undulations of growth, and under the 

 glass with minute concentric and longitudinal striae. 



This species approaches the L. Bavisii (Mc Coy) of the Lingula 

 Flags in Wales, but that species is a shorter and broader form, 

 with an apical angle of from 95° to 100.° It is also closely al- 

 lied to L. attenuata, (Sowerby) but according to the figures in 

 Siluria, that species is smaller and more of an oval shape. 



Each valve has three plane faces, the central one of which 

 commences at the beak and gradually widens to the front. The 

 other two slope to the lateral margins. In some specimens there 

 is an obscure longitudinal ridge along the middle, running from 

 the beak to the front. In a longitudinal section the valves are 

 gently arched, the greatest convexity being nearer the beak than 

 the front. 



Locality and formation. — The most perfect specimens were 

 collected on the island of St. Joseph in Lake Huron, in strata, 

 which, from their holding Columnaria alveolata, I think must be 

 regarded as of the age of the Black River Limestone. It also 

 occurs near L'Orignal in the undoubted Chazy limestone, associ- 

 ated with Rhynconella plena. Professor Hind of Trinity College, 



Canadian Nat. * Vol. IV. No. 6. 



