No. 6.] J. W. DAWSON — SILURIAN FOSSILS. 341 



NOTES ON FOSSILS. 



A few of the species observed are new, and concerning others 

 new facts were brou2;ht out in the examinations made. The 

 more important of these points are referred to below. 



Chaetetes or Stenopora and Chidopora. — Two branching corals 

 referable to these genera are very abundant in the East River 

 "beds, and the former also occurs plentifully at Arisaig. The 

 former is a coral of the family Chaetetldce^ very closely resem- 

 .bling S. fibrosa, but the specimens are not in such a condition as 

 to permit a close comparison. The latter is found only in the 

 state of casts, and is a large-celled species resembling C. fibrosa 

 of Hall. 



Stricklandinia Billhigsiaiia, n. s. 



This is a large shell, 6 centims. in breadth and 4 in length, 

 with a pointed beak and the sides spreading at an angle of about 

 120^ to the broadly rounded lateral corners, which are united 

 by a nearly straight margin. The surface presents unequal lines 

 of growth, and in the middle of the dorsal valve is a low flat 

 ridge with a slight furrow in the centre. The ventral valve has 

 a corresponding flat sulcus. This shell is closely allied to L. 

 Davidsoni, Billings, from the Upper Silurian of Gasp^, but is 

 much broader in form. 



Stropliomena Gilpini, n. s. 



Shell, when full grown, nearly an inch in diameter; length 

 and breadth nearly equal ; hinge line equal to breadth ; valves 

 little elevated ; hinge area narrow. Surface marked with nume- 

 rous fine radiating elevated lines, between which others are intro- 

 duced as they diverge from the beak. When the surface is well 

 preserved microscopic concentric striae are seen to cross the 

 radiating lines, and when the outer surface is removed the struc- 

 ture of the shell appears punctate. Muscular impressions oval, 

 elongate and narrow. This shell is very abundant near the 

 Sutherland River ore-bed. It appears to difi"er from any de- 

 scribed American species, but in general form and the style of 

 the muscular impressions resembles S. oriiatella of Salter from 

 the Upper Ludlow of Britain, though it has finer and sharper 

 superficial sculpture. 



