598 K. ETHEEIDGE ON THE PALAEONTOLOGY OE THE 



tamerus-limestone. M. tumida is a Scandinavian as well as a 

 .British species ; the American form is usually referred to M. 

 Mariw, and occurs in the Niagara group. Our species, " M. 

 tumida" is known in Britain, Gothland, Bohemia, and New- York 

 State; we now record it from the Polar area, associated with 

 Wenlock forms. 



Genus Stkophodonta, Hall*, 1852. 

 Stkophodonta Eeildeni, Ether. (PL XXY. fig. 4.) 



Of this gigantic shell we have only the ventral valve. It is pro- 

 bably the largest species of Strophodonta known (if it be Strojpho- 

 donta) ; it measures 4 inches along the hinge-line by 3 inches in depth. 

 Our single valve may almost be definitely referred to S. magnified 

 of Hall ; but owing to its structure being badly preserved its identity 

 may be doubtful ; this also prevents my seeing the crenulated hinge- 

 line characteristic of the genus : I name it, however, after Captain 

 Eeilden, who so carefully collected the many specimens brought 

 home from the Expedition. 



Shell very large, semielliptical, rounded at the extremities of the 

 hinge; hinge-line nearly straight or slightly sloping from the 

 umbo to the two extremities, less than the width of the shell, 

 which is about 4 inches ; umbo very small ; concentric lines of 

 growth are traceable ; also longitudinal impressions or remains of 

 slender ribs passing from the umbo to the ventral margin, but 

 not so pronounced as in the genus StreptorJiynchus. I know of 

 no shell in the European Palaeozoic rocks at all resembling this 

 species. The genus is well represented in the Lower Helderberg 

 and Oriskany series of New York, no less than thirty-four species 

 being known to the State geologist. Our specimen might almost 

 be regarded as a gigantic Orthis or Chonetes. I, however, prefer re- 

 ferring it to Strophondonta. 



Hall's species, S. magnifica, occurs in the Oriskany Sandstones 

 (Lower Devonian) of New York and Maryland ; -other species occur 

 in the Hamilton group, Iowa. 



Log. Cape Hilgard, lat. 79° 41'. Upper Silurian. 



Class LAMELLIBRANCHIATA. 



Not a single species of this class has occurred in the Silurian or Car- 

 boniferous series under examination ; and, singular as it may appear, 

 no bivalve shell has been collected, so far as I can ascertain, by any 

 previous Arctic expedition either from rocks of the Silurian, Devonian, 

 or Carboniferous series : yet it cannot be supposed that no forms of 



* A group of Strophomenoid shells possessing a crenulated binge-line and no 

 foramen in the ventral valve ; the valves closely interlock, and the two valves 

 closely follow each other. 



