256 MAZATLAtf UNIVALVES 



spiral ribs, a taller spire, and a yellow mouth. These charac- 

 ters do not always go together, and are each extremely variable, 

 as are also the rugse on the colmnellar lip, it being difficult to 

 find two specimens exactly alike. The fineness of the ribs 

 sometimes differs in different parts of the same shell. The 

 colour within presents all shades from a brilliant orange to pure 

 white. The sharp labral margin, (crenulated by the ribs,) is 

 either black throughout, or tessellated with light between the 

 ribs. Spire always more or less eroded, even in young speci- 

 mens, which in this collection were extremely rare. These are 

 known from the next species by the non-granular lip (smooth 

 in the youngest specimen,) strong teeth, and raised spire. 

 Costse often scarcely scabrous. Labrum thickly callous within 

 the margin, dentate, with very strong teeth at the extremities. 

 Hugse often continued on the spire, beyond the flattened colu- 

 mella. Operculum (in both the forms IS", ornata and N. 

 Deshayesii) outside finely granular, with an obscure spiral line 

 marking off about a quarter of the shell from the outside, and 

 ending in a deep sinus on the inner margin. Tooth stoutly 

 projecting, curved downwards opposite the not inconspicuous 

 spiral apex. Colour orange brown, A few were found loose, 

 with the spiral line scarcely developed, and of a more ashy 

 colour. As there was no other large species of Nerita among 

 the shells, these are presumed to be of abnormal growth. The 

 following shells, selected from but a small stock, exhibit the 

 principal variations in the wrinkling near the second of the 

 four teeth : to display all the minute differences would have 

 been to retain almost every specimen. The shells are not 

 nearly so large as further down the coast ; the largest measur- 

 ing only long. I'll, lat. 1*18, div. 110 120. 

 Hob. Is. of Timor ; sp. typ. Lam. teste E/ecluz. [?] Real 

 Llejos, Sowerby. Panama ; very common, on rocks, especi- 

 ally in crevices, between high water and three-quarter tide ; 

 young crawling above high water mark on rocks and stones 

 wet with spray ; C. B. Adams S. W. Mexico, P. P. C- 

 Mazatlan ; not common ; L'pool fy Havre Coll. 

 Tablet 1181 contains 4 sp. of different ages: 'the smallest, 

 ' 48 across, displays an orange spire, smooth at the apex, with 

 distant ribs, intercalary ones appearing at the margin. 1182, 

 1 sp. ribs distant, form ornata. 1183, 1 do., ribs changing, in 

 part very close, form Deshayesii. 1184, 2 sp. displaying col- 

 oured lip; one with a single orange spot, the other richly 

 tinted, inside and out, with spire abnormally elevated. 



