I 



MAZATLAN UNIVALVES 341 



doubt, simply because the Mazatlan shells were not mimerous 

 enough to oppose, while they did not confirm, his arrangement. 

 While in Cerithiopsis, the sculptxire is tolerably constant, in 

 these, as in the British species, the rows of nodules and the 

 convexity of the spire outlines vary in arrangement on the 

 same spechnen according? to age. The basal sculpture does 

 not appear in the young shell. 



391. Teifobis alternatus, C B. Ad. 



Pan. Shells, no. 207, pp. 158, 310. 



Shell with the first 7 whirls transparent, light horn- coloured ; 

 the first two smooth, then with numerous radiating lines, 

 crossed by first one, tben two, then three spiral ridges, which 

 gradually become nodulous. Then of a purplish brown, for 

 many whirls with two rows of stout, lighter-coloured nodules. 

 Between these a fine liae appears which gradually develops 

 into first a smaller and at last an equal sized row of nodules. 

 Below are one keel on the periphery and two on the base. 

 The colour changes to whitish on the lower portion of the later 

 whirls. The shell is comparatively large, a fragment measur- 

 ing "OS across. A specimen with 9 normal whirls measures 

 long. 'VI, long. spir. '14, lat. "055, div. 20". 

 ^a5.— Panama, 5 sp. C. B. Adams. — Mazatlan ; portions of 



8 sp. off" Spondylus ; L'pool Col. 



Tablet 1614 contains a very young sp., a perfect adolescent 

 one, and a fragment of an adult. 



392. Teifobis inconspicutjs, C. B. Ad. 



Pan. Shells, no. 208, pp. 159, 310. 



Shell in sculpture closely resembling T. alteruatus, but much 

 smaller ; with the nuclear whii'ls shorter in proportion, light 

 coloured only at the apex, developing the nodules and the dark 

 colour earUer and more gradually. Colour dark throughout ; 

 the last two whirls with 3 complete rows of nodides. Anterior 

 spiral ribs larger, that on the peripherj' sometimes sUghtly 

 scidptured. A specimen very perfect at the mouth but with 

 the apex deficient, measures long. '15, long. spir. "115, lat. "05, 

 div. 18". 

 Hah. — Panama ; 16 sp. under stones near low water mark ; 



C. B. Adams. — Mazatlan ; 12 sp. more or less complete, off" 



Spondylus and Chama ; L'pool Col. 



