522 



MOLLUSCA 



PHYLUM VI 



Gonradella U. and S. (PhragmoUtes Conrad) (Fig. 847, D, E). Ordovician and 

 Silurian. 



A 1! C 



Fig. 847. 



A, B, Bucania haüi Ulr. and Scof. Ordovician ; Minnesota. C. Salpingostoma hudli (Whitf.). Ordovician ; 

 Illinois. D, E, Conradella fimbriata Ulr. and Scof. Ordovician ; Minnesota. 



Tetranota U. and S. Like Bucania, but witli four dorsal ridges. Ordovician 

 and Silurian. 



Kohenia U. and S. Ordovician. Megalomphala Ulr. ; Oxydiscus Koken. 

 Ordovician to Devonian. 



Family 7. Bellerophontidae M'Coy. 



Symmeti'ical, involute shells with rapidly enlarging wJiorls, mouth expanded 

 laterally and ventrally hut not dorsally ; umhüicus small or closed ; inner lip thickened, 

 outer ivith a short slit ; slit band always present ; surface with lines of growth only or 

 cancellated. Cambrian to Triassic. 



The Bellerophontidae were classed by Montfort with the Cephalopoda ; by Deshayes, 

 on accoimt of their resemblance to Atlanta, with the Heteropoda ; and by de Koninck 



with the Aspidobranchiates. The 

 thick Shells sometimes retain traces 

 of their original pigmentation. At 

 least 300 Paleozoic species have 

 been described.' 



Bellerophon Montfort (Fig. 848). 

 Distinguished by : (1), the absence 

 of sculpture save the lines of 

 growth ; (2) the small or entirely 

 closed umbilicus ; (3) the moderate 

 expanse of the aperture ; (4) the 

 callosity on the inner lip, and (5) 

 a well developed slit band terminat- 

 ing in a slit in the outer lip. Or- 



Fio. 848. 



BelleropJion bicarenus Leveille. Lower Carboniferous ; 

 Tournay, Belgium. 



dovician to Permian, maximum in Carboniferous, 



Patellostium Waagen. Like Bellerophon, but aperture greatly expanded. Devonian 

 and Carboniferous. 



