474 PROCEEDINGS OF THE ACADEMY OF [1899. 



front; the latter half of the base becoming greatly swollen, the 

 umbilicus passing into a large excavated area behind the columellar 

 lip. Aperture very oblique, squarish oblong, white within ; peris- 

 tome well expanded, the upper and baso-columellar margins 

 straightened and subparallel, the latter reflexed, dilated and quite . 

 vaulted over the umbilicus at the insertion; parietal callus bluish 

 white, strong. 



Alt. 48; greater diam, 51, lesser 45 mm. 



A single specimen was found in a collection obtained by Mr. 

 Walter F. Webb, of Albion, N. Y., in whose honor the species is 

 named. It bore the label ^' Helix, Solomon Is.;" but I regard 

 this locality as open to grave suspicion. It is probably from 

 northern Queensland, though one would scarcely expect a new 

 Helix over two inches in diameter from that region, after the labors 

 of Dr. Cox, Messrs. Brazier, Hedley and others in the elucidation 

 of the Queensland fauna. 



T. Webbi belongs between the Hadra section of Thersites and 

 the typical group of the genus, but is nearer the former. It 

 resembles T. bipartita in the bicolored shell substance, readily seen 

 by looking in the aperture with the shell held toward a light, in 

 the structure and color of the lip, and the form of the latter part 

 of the base of the shell and tfie umbilicus. It differs from T. 

 bipartita in the strong peripheral keel, flat whorls of the dome- 

 shaped instead of conic spire, the greater anterior deflection of the 

 last whorl, the less rotund aperture and the darker color of the 

 cuticle above. T. Webbi vesemhles Thersites richmondiana in being 

 keeled, and in the flatness of the whorls of the spire, separated by 

 merely linear sutures; but it differs in other particulars of form, 

 color, etc., so much that a comparison is needless. 



