338 AMERICAN JOURNAL 



nodulous. Principal ribs about 16, of which the anterior 

 are small, and generally abraded; but very irregular in ar- 

 rangement. Sometimes 5, sometimes 12, divide the posterior 

 half of the margin. Apex generally the full height of the 

 shell; sometimes quite over the anterior margin, in which 

 case the shell is generally elongated, and becomes the digitalis 

 of Eschscholtz ; sometimes only at one-sixth, or even one-third 

 of the length. Color, outside white, with irregular stripes of 

 brown, covered with a thin layer, spotted with olive-brown, 

 which is generally eroded. Inside white or brownish-yellow ; 

 generally with an irregular brown spot, which is very rarely 

 striped, and is sometimes entirely absent. Margin moderate, 

 irregularly spotted with dark brown or black; very rarely 

 without spots. Dr. Gould's description of his P. scahra ex- 

 actly accords with this species, as does theshell^ at fig. 456^.; 

 but great confusion has arisen from the other specimen,* fig, 

 ■456, 456a belonging to a different species=^l. spectrum, Nutt. 

 The name is retained for the shelP to ivhich tlie diagnosis applies, 

 and, therefore, may be discarded as a synonym. This fortu- 

 nate circumstance prevents the further confusion which Avould 

 have attended the discarding of Keeve's Nuttallian species 

 with the same name. In the young shell, the apex is very 

 near the margin, and the back much arched. 



2. Var. umbonata, Nutt. This is the usual Southern form, 

 distinguished by the narrowness and small size of the ribs, 

 which scarcely interrupt the margin. They are from about 

 15 to 26, with much wider interspaces. ]3eing apparently 

 still- water shells, they display the lace-pattern of dark olive 

 and white, in very fine dots, with very beautiful effect. But 

 this is often suddenly interrupted, and the typical stripes seen 

 underneath. The interior is colored as in the typical form, 

 but generally with more of black in the margin. The shape 

 is still arched, but the shell is broader, and the apex is gene- 

 rally (not always) rather further removed from the margin. 



3. Var. textilis, Gld. This is an extreme form of var. wmZ/o- 

 nata, in which the sides spread out, the apex is nearer the 

 centre, the back is not arched, and the ribs are rounded and 

 distant. It can scarcely be distinguished from the young of 

 some of the varieties of yl.j3e/i!a, except by the fretted pattern. 

 It is probable that Dr. Gould had specimens of the latter 

 under his eye, intermixed, when he wrote the diagnosis, al- 

 though the figured type accords best with A. persona, var. 



* All the remarks on Dr. Gould's species are written after very careful 

 study of the figured types in the Smithsonian Institution ; those on Nut- 

 tail's species of the types in his own collection (since presented to the 

 British Museum) ; those on Reeve's species of the types in Mus. Cuming, 

 now removed to the British Museum ; and those on D'Orbigny's species*, 

 of the types in his own collection ija the British Museum. 



