MAZATLAN UNIVALVES 179 



patches often shewing through ; the sharp purplish outer lip, 

 well armed with white ridges within, in the young shell, which 

 afterwards develope strong teeth at the ends, and are last of 

 all absorbed ; and the thin inner lip, which developes one 

 strong transverse parietal plate between two small denticles 

 (others being just discernable in the young shell), and one 

 large slanting columellar fold, which winds round the base of 

 the pillar, making an umbilical chink. A few extremely faint 

 spiral striae are sometimes seen on the epidermis, near the 

 base and above the bluntly angled shoulder. Long. '65, 

 long. spir. "11, lot. '38, mean div. 110. 

 Hab. Mazatlan, Lieut. Shipley, Do. ; not uncommon; 



L'pool Col. 



Tablet 812 contains 9 sp. normal state. 813, 4 do. dark 

 variety. 814, 4 do. light var. 



FAMILY LIMNEID^E. 

 GEN-US APLEXA, Flem. 



Hist. Er. An. 1828, p. 276. Gray, Proc. Zool. Soc. 1847, 

 p. 180 : do. Turt. ed. ii. Beck in Phil. Handl. Conch. 

 p. 255. 



Bulinus, Adanson, teste Gray Fig. Moll. An. 1850, p. 119. 

 H. fy A. Ad. Gen. vol. ii. p. 259. JSTon Bulinus, Adanson, 

 teste Gray, Proc. Zool. Soc. 1847, p. 180, nee Seek in Phil. 

 Sandb. Conch, p. 255 : nee Bulinus, Soio. 



Physa, pars, auct. Mantle simple edged. The shells of this 

 section indicate affinity with the A. hypnorum, the animal 

 of which is sufficiently distinct from the typical Physee. The 

 species in this genus are extremely difficult to distinguish, 

 especially in the young state. The naturalist has to rely 

 principally on the general habit, individual characters being 

 subject to variation. 



J 236. APLEXA AUEANTIA, n. s. 



A. t. tenui, ovatd, Icevigatd seu striis incrementi exillimis, 

 nitidd, aurantio-corned, ad spiramfuscd ; spirdparvd, in adult a 

 semper erosa; anfr. circiter vii., subplanatis, twmidis ; aperturd 

 satis dilatatd ; labio tenuissimo arcuato ; columella vix plicatd. 

 Physa Peruviana, Wee. in Zeit.f. Hal. 1850, p. 163, no. 6 : 



P. P. C. Cat. Prov. : non Gray, Spic. Zool. p. 5, pi. 6, f. 10. 



