Pulmonifera of Maine. 45 



slightly inclined to the left ; slopes irregular, caused by different 

 periods of repose and growth ; posterior slope in most specimens 

 straight, anterior slope convex, lateral slopes steep ; shell widening 

 anteriorly ; lines of accretion extremely fine, visible within but 

 requiring a magnifier to discern them without, being greatly 

 obscured by fine grains of sand agglutinated to the surface. 

 Periostraca pale yellow, the surface when magnified exhibits about 

 fifty-five delicate ribs, which radiate from the apex to the periphery 

 of the shell. Length .12 inch, breadth .10 inch, height .06 inch. This 

 species w^as discovered by John M. Gould, in the Androscoggin 

 River, at Bethel, Me., in 1854. I have since found it in the above 

 locality clinging to the under side of stones near the shore, in 

 positions where it could in no way reach the surface of the water. 



Ancylus borealis. nov. sp. {Figs. 103, 104.) 



Shell elliptical, solid, light yellow, apex elevated, rounded, very 

 obtuse, nearer the posterior margin of the shell ; ^-^"^ 



lateral slopes steep, anterior slope slightly 

 convex, near the apex ; posterior slope straight. .-.-r---. 



Fine regularly interrupted radiating lines mark ^.^ — -\ 

 the surface of the shell from the apex to the r ,, A 



borders: incremental lines irregular. Length V : ^J' 



.14 inch, breadth .09 inch, height .06 inch. ^-^.^r-^ss^Ws^afe^ 



This species resembles A. tardus in its general {Figs. 103, 104.) 

 form. It is much smaller however, and has a strong heavy shell. 

 Discovered by John M. Gould at Patten, in the northern part of 

 the State. 



VIYIPARID^. 

 Melantho decisa, Say. 



Abundant throughout the State, though the shell never attains 

 that size and perfection which characterize the same species in 

 the western states. Heterostrophed specimens are frequently 

 met with in embryo. 



The lingual membrane examined in one specimen of this species 

 presented the singular anomaly of eight laterals thus, 4-1-4, the 

 constant formula being 3-1-3. 



