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, lat. °38, mean div. 110°. 
Hab.— Mazatlan, Ineut. Shipley.—Do.; not uncommon; 
TP pool Col. 
Tablet 812 contains 9 sp. normal state.—813, 4 do. dark 
variety.—814, 4 do. light var. 
Famity LIMNEIDA. 
Genus APLEXA, Flem. 
Hist. Br. An. 1828, p. 276.—Gray, Proce. Zool. Soc. 1847, 
p. 180:—do. Turt. ed. 11.— Beck in Phil. Handb. Conch. 
p. 255. 
Bulinus, Adanson, teste Gray Fig. Moll. An. 1850, p. 119.— 
H. & A*Ad. Gen. vol. ii. p. 259.—Non Bulinus, Adanson, 
teste Gray, Proc. Zool. Soc. 1847, p. 180, nee Beck in Phil. 
Handb. Conch. p. 255 :—nec Bulinus, Sow. 
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 Physe. 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. 
236. APLEXA AURANTIA, ”. s. 
A. t. tenui, ovatd, levigatd seu striis incrementi exillimis, - 
nitidd, awrantio-corned, ad spiram fusca ; spird parva, in adulté 
semper erosd ; anfr. circiter vii., subplanatis, tumidis ; apertura 
satis dilataté ; labio tenuissimo arcuato ; columelld vie plicaté. 
Physa Peruviana, MWke. in Zeit. f. Mal. 1850, p. 163, no. 6 :— 
P,P. C. Cat. Prov.: non Gray, Spic. Zool. p. 5, pl. 6, f. 10. 
