MAZATLAN UNIVALVES 181 



Genus PLANOEBIS, GueUard. 



238. Planoebis tumens, n. s. 



P. t. rapide titmente, parvd, corned seu nifo-fuscii ; anfracti- 

 btis iv.-v., concentnce tenue striatis, striis undulatis ; sutwris 

 valde impressis ; latere altera prope sutitram suhangidato, seu, 

 interdiim subcarinato ; altero rotuhdato ; umhilico altissimo ; 

 aperliira margine sinuato, latere altero swpra extante, infra 

 compressa, altero supra planatd, infra producta, capaci, rotun- 

 datd ; lahio tenuissimo. 



Planorbis affinis, P. P. C. Cat. Prov. ; non C. B. Ad. in 

 . Contr. Conch, no. 3. p, 44. 



Planorbis tenagopliUus, like. Zeit.f. Mai. 1850, p. 163, no. 5 : 

 non BOrh., B. M. Cat. Moll p. 25, no. 234. 



This species is so variable that it is difficult to describe it so 

 as to include all the specimens and yet separate it from its 

 congeners. Aberrant individuals on the one side closely 

 approach P. affinis, on the other P. lentus, Say. The three 

 may hereafter be proved identical : but the general habit of 

 P. tumens, as gathered [from repeated examinations of many 

 hundred specimens, is sufficiently distinct from the Jamaica 

 species. The whirls are more rapidly enlarging, more swollen, 

 and the lip more shoiddered. An unusually large specimen 

 measures long. '63, lat. '58, alt. '27. 



Hah. — Mazatlan ; not uncommon ; Upool Col. 



Tablet 824 contains 3 sp., deep narrow umbilicus. — 825, 5 do. 

 ordinary state.— 826, 4 do. umbdical suture large— 827, 4 do. 

 umbilicus flattened.— 828, 3 do. base rounded. 



Tablet 829 contains 3 sp. reddish brown var., spi'eading. — 

 830, 3 do. ordinary state.— 831, 3 do. keeled. 



Tablet 832 contains 7 sp. distorted growth. 



Order THALASSOPHILA. 



Family SIPHONARIADiE. 



Genus SIPHONAEIA, Gray. 



Gray in Sow. Gen. part xxi. \%%i.—Blainv. Diet. Sc. Nat. 



vol. xxxii. p. 267. 

 Mouretia, (Gray) Sow. 1835.— Trimusculus, Schmidt, 1832. 

 April 1856. r 



