GASTEROrODA. 345 



Fossil, 128 species. Lower Silurian — Carb. North America, 

 Europe, Australia, India. The name Bucania was given by 

 Hall to the species with exposed whorls ; in B. expansus, PI. 

 XIV., Fig. 28, the aperture of the adult shell is much expanded, 

 and the dorsal slit filled up. (Salter.) 



BeUerophina, D'Orbigny (not Forbes), is founded on the 

 Nautilus minutus, Sby. PI. XIV., Fig. 26, a small globular 

 shell, spirally striated, and devoid of sej)ta. It is found in the 

 gault of England and France. 



Cyrtolites, Conrad. 



Type, C. ornatus, PI. XIV., Fig. 30. 



Etymology, kurtos, curved, lithos, stone. 



Shell thin, symmetrical, horn-shaped or discoidal, with whorls 

 more or less sej)arate, keeled, and sculptured. 



Fossil, 13 species. Lower Silurian — Carb. North America, 

 Europe. 



? Ecculiomphalus (Bucklandi), Portlock, PI. XIV., Fig. 31. 

 Lower Silurian, Britain, United States. Shell thin, curved, or 

 discoidal with few widely separate whorls, slightly unsym- 

 metrical, keeled. 



fig. 142. Maclurea Logani (Salter), L. Silurian, Canada. 



PMacltjeea, Lesueur. 



Named after William Maclure, the first American geologist. 



Shell discoidal, few-whorled, longitudinally grooved at the 

 back, and slightly rugose with lines of growth; dextral side 

 convex, deeply and narrowly perforated ; left side flat, exposing 

 the inner whorls ; operculum sinistrally sub-spiral, solid with 

 two internal projections (t t), one of them beneath the nucleus, 

 very thick and rugose. 



Fossil, 5 species. Lower Silurian. North America ; Scotland 

 (Ayrshire, M'Coy). 



This singular shell abounds in the " Chazy " limestone of 

 the United States and Canada; sections of it may be seen 

 even in the pavement of New York ; but specimens are very 

 difficult to obtain. We are indebted to Sir W. E. Logan, 

 of the Geological Survey, Canada, for the opportunity of 



q3 



