COASTS VISITED BY THE AKCTIC EXPEDITION - . 595 



valves much greater than either in Pentamerus galeatus or P. 

 ohlongus ; fissure not seen ; lateral margins smooth, anterior margin 

 nearly straight or faintly rounded ; surface of both valves nearly 

 smooth or concentrically marked, some specimens more strongly 

 than others. 



Our shell differs from Pentamerus galeatus in the absence of ribs 

 upon the mesial fold of both valves, and the wavy crenulations 

 upon the lateral portions of the shell, and also in the much wider 

 umbonal space between the two valves. P. Verneuili, Hall, from 

 the Lower Helderberg, is a strongly ribbed shell, and the umbo is com- 

 pletely hidden. Prom Pentamerus Knightii our species differs in 

 the want of ribs ; but in shape the valves of the two species fairly 

 agree. "We have no specimens showing the interior ; seven specimens 

 occur. 



Log. Offiey Island, lat. 81° 16'. From Upper Silurian, probably 

 "Wenlock Limestone. 



Pesttameeus, sp. 



This specimen occurs on a block of limestone of considerable size, 

 said by Captain Feilden to have been obtained from a drift boulder 

 in lat. 82° 30', at an elevation of 40 feet above the sea. This ventral 

 valve I have called Pentamerus ; it closely resembles P. conchidium, 

 Dalm. In drift boulder, lat. 82° 30'. 



Genus Rhynchonella, Fischer, 1809. 

 Rhynchokella nucula (Sow.). 



Terebratula nucula, Sow. Sil. Syst. t. 5. f. 20. 



Only one species of the genus occurs in the collection. It agrees 

 with the above species, so far as I am enabled to determine from 

 one specimen ; at all times a troublesome shell, and in every variety, 

 it has the widest distribution, in Britain occurring in almost every 

 locality where the Upper Silurian occurs, from the Llandovery rocks 

 upwards, ceasing only in the Upper Ludlow. 



Log. Bessels Bay, lat. 81° 6'. Upper Silurian. 



Genus Chonetes, Fischer, 1837. 

 Chonetes steiatella (Dalm.). 



Orihis striatella, Dalm. Kongl. Svenska Ak. Handl. 1827, p. Ill, 

 t.l.f. 5. 



Lepteena lata, Sow. Sil. Syst. p. 610, t. 5. f. 13. 



Chonetes striatella, Dav. Monogr. Sil. Brach., Pal. Soc. p. 331, t. 49. 

 f. 23-26. 



One individual only ; but it is nevertheless enough to declare the 

 presence of this common shell, which in Britain everywhere highly 

 characterizes the Wenlock and Ludlow rocks. The hinge-spines are 

 worn or denuded away (as is generally the case), but the other 

 characters are well preserved. 



