182 MAZATLAN UNIVALVES 



This remarkable genus does not appear to be rich in species 

 at Mazatlan. The magnificent S. gigas (? + char act eristica), 

 though traveling as far north as S. W. Mexico, where it is not 

 uncommon - (P. P. C.) y was entirely absent (adult) from this 

 collection. 



239. SIPHONAEIA LECANIUM, Phil. 



S. t. parvd, plerumque ovatd, interdum subdrculari^ ad cana- 

 lem projiciente ; subconwd, sen valde depressd ; cinered, fusca, 

 var'ie pictd ; epidermide tenui, adharente ; costis <zqualiter seu 

 inosqualiter distantibus, subacutis seu, valde rotundatis, inter- 

 stitiis s&pius costulis instructis ; costis majoribus xii. -xxii. ; 

 costis et costulis tenuissime striatis, striulis radiantibus, sub- 

 rugulosis ; costis et margine interno interdum albidis ; vertice 

 -subcentrali, Icevi, planatd ; pagind \interna sen atrd, sen fused, 

 raritys pallidd, rarissime vires cent e ; margine sen irregulariter 

 crenulato sen stellato ; costis rotundatis excurrentibus ; canali 

 declivi. 

 Phil, in Zeit. f, Mai. 1846, p. 51, no. IS.Menfo in Zeit.f. 



Mai. 1847, p. 177, no. 1. diagnosi aucta. Nunc diagnosi 



valde aucta. 



It cannot be expected that any one should recognize this 

 species from so comprehensive a description ; and yet any 

 narrower Definition would shut out shells that I am unable 

 to separate from the typical forms. In its ordinary state the 

 shell is subconical, thin, with a variable number of irregularly 

 disposed, rather sharp ribs, somewhat projecting, and generally 

 rubbed, shewing a white surface underneath. Between these 

 ribs are an equally variable number of riblets, not projecting ; 

 and over the whole surface, ribs included, are microscopic 

 striae. When the creature grows in sheltered situations, it 

 spreads out, becomes flat and large, the ribs ^swell, become 

 rounded, and develop at the margin into beautiful palmations. 

 So different is this form from the usual one that if they were 

 each at all constant in their characters, no one would suspect 

 them of being identical. Yet the variations in each are so 

 extraordinary, and the intermediate forms so numerous, that 

 I have found it impossible to separate them. Often, both in 

 the flat and conical forms, the riblets develop into principal 

 ribs, until ail are nearly of the same size. It then closely 

 approximates the next species. Interior of a rich iridescent 

 brown or brownish black, generally light at the margin, some- 



