386 MOLLUSCA. 
Planorbis ancylostomus, var. B. strebelianus, Fisch. & Crosse, Miss. Scient. Mex., Mollusca, li. 
p. 63 (1880) *. 
Shell rather large, with more gradually increasing whorls and more funnel-shaped appearance of the 
right side. 
Hab. EB. Mexico: Laguna de Los Cocos, Rio Tenoya and ditches and channels 
adjoining it, all in the environs of Vera Cruz (Strebel 16 17). 
2. Planorbis wyldi. (Tab. XXI. fig. 5, very young shell.) 
Planorbis tumens (Carp.), Morch, Malak. Blatt. vi. p. 112 (1859) !; Fisch. & Crosse, Miss. Scient. 
Mex., Mollusca, ii. p. 62 (part.), t. 82. figg. 4, 4a, 0,'¢ >, 
Planorbis wyldi, Tristram, P, Z. 8. 1861, p. 232°. 
Planorbis tenuis (Phil.), v. Mart. P. Z. S. 1875, p. 649 *; Biolley, Moluse. terr. y fluv. de Costa 
Rica, p. 16°. 
Planorbis tenuis, var. wyldi, Fisch. & Crosse, Miss. Scient. Mex., Mollusca, ii. p. 62, t. 34. fig. 2°. 
Planorbis salvinii, Clessin, in Martini & Chemnitz, Syst. Conch.-Cab. ed. 2, Limnzeiden, p. 207, t. 31. 
fig. 8 (1886) ”. 
Planorbis sp., Stoll, Reisen und Schild, Guatemala, p. 33 (1886) °. 
Very like a small P. tenuis, from which it differs in having the whorls increasing a little less rapidly and on 
the right side usually rather more swollen; the aperture in full-grown specimens is formed as in typical 
P. tenuis, in younger ones more rounded. 
a. Diam. maj. 15, min. 12, alt. 8; apert. diam. 7, ampl. 8 millim. 
b. ” 14, ,; ll, ,, 73 ” 63, ” 4 ” 
C. ” ll, 9, 6; ” 5, 95 6 ” 
a. The largest of Salvin’s specimens, from Duefias ; 6. Apparently full-grown specimens from Rio Reventazon, 
Costa Rica; c. From Fischer and Crosse’s figure. 
Hab. N. Guatemata: Coban, in ponds (Bocourt?; Stoll). 
CENTRAL GUATEMALA: Plateau (Llano) of Guatemala, in shallow ponds and lagoons 
of Naranjo § and Aceituno (Szo/0). 
W. Guatemata: Lake of Duefias (Salvin®; Stoll), Santiago de Zamora (Salvin). 
S.W. Nicaragua: near the Volcan de Mombacho (Orsted '). 
CENTRAL Costa Rica: common in the environs of San José, in the rivers Tiribi and 
Torres (Biolley °). 
E. Costa Rica: Rio Reventazon, at Ujarras (Biolley®); valley of the Alta Coca, 
near Talamanca (Pittier). 
S.W. Costa Rica: along the Diquis river, below Terraba (Pittier). 
The examples from the valley of the Alta Coca, Costa Rica, are very small, measuring 
6 millim. only in diameter, and it is difficult to say whether they are full-grown or 
young. On the contrary, among the specimens collected by O. Stoll at Duefias there 
varieties of the North-American P. trivolvis this shell differs in the less distinct rib-like sculpture, the pale 
? 
greyish (not yellow or brown) colour, the more flattened middle part of the left side, and, in many specimens 
the more asymmetrical shape of the aperture. 
