COASTS VISITED BY THE AECTIC EXPEDITION. 603 



Point, lat. 79° 42', and Cape John Barrow. They resemble forms 

 common in the Ludlow, Wenlock, and Upper Silurians generally 

 of Britain, especially H. gregaria ; no characters occur to distinguish 

 them ; but the entire peristome and numerous gradually increasing 

 smooth whorls leave no doubt as to the genus. None are suffi- 

 ciently well preserved to enable me to describe them ; their strati- 

 graphical value is also lost owing to their being drifted specimens. 

 Orthoceras, Strojphomena, Bhynchonella, and Macrocheilus occur on 

 the slabs. 



Log. Hayes Point, lat. 79° 42', and Cape John Barrow, lat. 79° 48'. 



Genus Aceocttlia, Phillips, 1841. 



ACEOCTTLIA HALIOTIS (Sow). 



Nerita haliotis, Sow. Sil. Syst. t. 12. f. 16 ; Murchison, Siluria, 

 t. 24. f. 9. 



Many examples of this shell are in the collection, and, as usual, as 

 many varieties ; for no two are alike. A. prototype Phill., may 

 in some cases be referred to A. haliotis (Sow.) ; but, as a rule, it is 

 naticoid rather than neritoid in form. Capt. Feilden's specimens 

 are in excellent preservation; and although so much variation is known 

 to occur in the species of this group, yet I am disposed to refer 

 some specimens to a new species to be next described. A. haliotis 

 occurs at Bessels Bay and Dobbin Bay (lat. 79° 40'), and is widely 

 distributed, ranging from Bohemia and Thuringia to Britain and 

 Ireland ; and I believe the specimens collected by Dr. Coppinger are 

 the same species. No less than eighty species are known in the 

 Silurian rocks of the two hemispheres, recorded under the names 

 Capreolus, Platyceras, Pileopsis, and Acroculia. Forty species are 

 American and twelve German ; the remainder are distributed 

 generally through the European Silurians. 



Genus Plattceeas, Conrad, 1840. 



Plattceeas naticoides, Eth. (PL XXYII. figs. 4, 4a.) 



I cannot find any species of Platyceras or Acroculia answering to 

 this, which I term P. naticoides from its extreme resemblance to 

 many species of that genUs as well as many forms of Platyostoma ; 

 but, strong as is the general resemblance, still the apex of the spire, 

 indented suture, and abnormal body-whorl remove it from Acro- 

 culia. The extensive genus Platyceras of Conrad receives forms so 

 varied and abnormal that almost any Palaeozoic naticoid shell may 

 be placed within its limits. Forty species are recognized by Hall as 

 coming chiefly from the Helderberg group of America. Our Upper 

 Silurian Platyceras has not occurred above the Silurian rocks of the 

 west. The genus Strophostylus of Hall may receive these thin shells 

 with expanded volutions (especially the last or ventricose body- 

 whorl) and small spires ; but I prefer referring them to Platyceras. 



/Sjp. char. Shell subglobose, somewhat elongate in the direction of 



