MAZATLAN UNIVALVES 18] 
Genus PLANORBIS, Guettard. 
238. PLANORBIS TUMENS, 7. Ss. 
P. t. rapide tumente, parva, corned seu rufo-fuscé ; anfracti- 
bus iv.-v., concentrice tenue striatis, striis undulatis ; suturis 
valde impressis ; latere altero prope suturam subangulato, seu 
interdum subcarinato ; altero rotundato ; umbilico altissimo ; 
apertura margine sinuato, latere altero supra extante, infra 
compressa, altero supra planatd, infra producta, capact, rotun- 
data ; labio tenuissimo. 
Planorors atinis, --P> PC)’ Cat. Prov. ; non .C. Be Adem 
Contr. Conch. no. 3. p. 44. 
Planorbis tenagophilus, Whe. Zeit. f. Mal. 1850, p. 163, no. 5: 
non D’Orb., 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 jfrom 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. 
Hab—--Mazatlan ; not uncommon; L’pool Col. 
Tablet 824 contains : 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. 
Orpver THALASSOPHILA. 
Famity SIPHONARIAD. 
Genus SIPHONARIA, Gray. 
Gray in Sow. Gen. part xxi. 1824.—Blainv. Dict. Sc. Nat. 
vol. xxxil. p. 267. 
Mouretia, (Gray) Sow. 1835.—Trimusculus, Schmidt, 1832. 
April 1856. ? 
