[MATTHEW] STUDIES ON CAMBRIAN FAUNAS 99 



GASTEROPODA. 



SCENELLA, Billings. 



SCENELLA cf. RETICULATA, Bill, 



cf. Scenella reticulata. Bill., Palaeoz. Foss., vol. il., pt. i,, p. 77 (no figure). 

 Scenella cf. reticulata. Bill., Nat. Hist. Soc, Bull, xviii., p. 190. 



Some shells which appear to be of this species were observed ; they 

 have campanulate apertures, and are of about the dimensions of Billings's 

 species. 



Sculpture. — The radial ornamentation is not properly described by 

 the term strife ; the radii are actually sharp thread-like ridges, with flat 

 intervals of considerable width between ; these, without break, cross over 

 fine striae of growth with heavier growth lines at intervals. These heavier 

 concentric lines in connection with the radial lines give the shell the can- 

 cellated appearance to which it owes its name. 



Size. — The largest individual observed had an aperture 7x9 mm. 

 across. 



Scenella cf. retusa, Ford. 



cf. Scenella retusa, Ford, Am. Jour. Sci., 3 ser., vol. v., p. 213, figs. 2a, b (p. 214). 

 Scenella cf. retusa. Ford, Nat. Hist. Soc, Bull, xviii., p. 190. 



Another species of Scenella appears to agree in most respects with 

 Ford's species, above cited. It is smaller than S. cf. reticulata and is 

 distinguished by its ornamentation. It possesses the two radiating ridges 

 diverging from the apex, supposed to be characteristic of the species, 

 but the surface characters do not altogether agree with Ford's description, 

 as the radiating Unes are more prominent than the concentric. 



Sculpture. — The surface is marked by radii broader than those of >S^. 

 of. reticulata, and less prominent. There are tine close strias of growth, 

 especially around the margin ; and more distant, somewhat irregular 

 concentric undulations of growth ; the two former varieties of sculpture 

 are obscured by a granulation of the surface of the shell, more distinct 

 than that of S. cf. reticulata. 



This species is commoner at Smith Sound than the preceding. 



RAXDOItllA. 



Among the forms common at Smith Sound is one which at first 

 view I referred to the genus Palœacmœa on account of its general form 

 and strong concentric ridges. On further investigation of Palœacmœa I 

 cannot find any species characterized by the strong radiating ridges which 

 in addition to the heavy concentric ridges, this species possesses. 



