MAZATLAN UNIVALVES 181 



GENUS PLAJSTORBIS, Guettard. 



j^ 238. PLANORBIS TUMENS, n. s. 



P. t. rapide tumente, parvd, corned seu rufo-fuscd ; anfracti- 

 bus iv.-v., concentrice tenue striatis, striis undulatis ; suturis 

 valde impressis ; latere altero prope suturam subangulato, seu 

 inter dum subcarinato ; altero rotundato ; umbilico altissimo ; 

 aperturd margine sinuato, latere altero supra extante, infra 

 compressd, altero supra planatd, infra productd, capad, rotun- 

 datd ; labio tenuissimo. 

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



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

 Planorbis tenagophilus, Mke. Zeil.f. Mai. 1850, p. 163, no. 5 : 



non D'Orb., S. 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 shouldered. An unusually large specimen 

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

 Sab. Mazatlan ; not uncommon ; L'pool Col. 



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

 ordinary state. 826, 4 do. umbilical suture large 827, 4 do. 

 umbilicus flattened. 828, 3 do. base rounded. 



Tablet 829 contains 3 sp. reddish brown var., spreading. 

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



Tablet 832 contains 7 sp. distorted growth. 



OBDER THALASSOPHILA. 



FAMILY SIPHONAEIAD^E. 



GENUS SIPHONAEIA, Gray. 



Gray in Sow. Gen. part xxi. 1824. Blainv. Diet. Sc. Nat. 



vol. xxxii. p. 267. 



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

 April 1856. r 



