134 BULIMULUS-ORTHOTOMIUM. 



This species approaches very near certain forms of B. dealbatus 

 var. mooreanus in some Texan localities, and is only with great 

 difficulty to be distinguished from them. Indeed some conchologists 

 of great experience with Texan Bulimuli regard alternatus as merely 

 a variety of dealbatus. My reasons for retaining B. alternatus dis- 

 tinct, are that differences though inconspicuous actually exist; that 

 throughout the range of alternatus it occurs with either mooreanus or 

 schiedeanus without intergrading in the vast majority of localities, 

 and that as ordinarily found, the species is conspicuously distinct. 

 It should be added that this opinion is based upon the study of 

 many hundreds of shells, and considerable field experience in 

 Texas. 



Typical ALTERNATUS, PI. 25, figs. 50, 51, 52, 53. 



As described by Mr. Say and represented by one of his types now 

 before me, differs considerably from the ordinary form of the 

 species. It is conic-ovate, not very thick, with 6 convex whorls 

 separated by impressed sutures. Alternately ragged-striped with 

 opaque white and blue-gray in dead shells, corneous-brown when 

 living ; aperture bluish-white inside (hence the " perlaceous tinge " 

 of Say's description). Columella concave, with no noticeable fold. 



Alt. 30i, diam. 18 ; length of aperture 16? mill. 



Mexico (Maclure). 



The synonym B. lactarius apparently belongs to typical alternatus. 

 Var. MARINE (Albers)." PI. 17, figs. 17, 18, 20, 12, 22-26. 



Ovate-oblong, thick and solid, smooth, with 6 to 7 moderately con- 

 vex whorls ; white or with brown streaks or ragged stripes ; aper- 

 ture dark brown within (rarely ochraceous) ; columella more or less 

 distinctly folded or toothed above. Dimensions and proportions 

 quite variable. 



Alt. 27, diam. 15 mill, (average specimen). 



Alt. 22, diam. 14 mill, (short specimen). 



Alt. 35?, diam. 17 mill, (long specimen). 



Texas: two or three tiers of counties north of the Rio Grande, from 

 Corpus Christi N.- W. to Frio and Val Verde Counties and south- 

 ward. Northeastern Mexico, at Matamoras and south to Tampico, 

 State of Tamaulipas. 



B. binneyanus Pfr., olim. is the same ; also " var. albidus Taylor/* 

 of Cockerell, which of course is utterly baseless. That the classifica- 

 tion of varieties proposed by Mr. Cockerell (Journ. de Conchyl., 



