PLANOBRBIS. 387 
is one measuring 18 millim. in diameter, and which forms therefore a connecting-link 
towards P. tenuis. 
Very young specimens (fig. 5), if turned the left side upwards, have much the 
appearance of a Physa, which is also the case in other species of the subgenus 
Helisoma: see my remarks on Planorbis scalaris from Florida (Sitz.-Ber. Ges. naturf. 
Freunde, Berlin, 1896, p. 16). 
3. Planorbis tumens. 
Planorbis tenagophilus (d’Orb.), Menke, Zeitschr. f. Malak. 1850, p. 163°. 
Planorbis tumens, P. Carpenter, Catal. Mazatlan Shells, p.81 (1857)?; Binney, Land and Freshw. 
Shells N. Am. ii. p. 106, fig. 180°; Fisch. & Crosse, Miss. Scient. Mex., Mollusca, ii. 
p- 62, t. 88. figg. 8, 3a*; ?Clessin, in Martini & Chemnitz, Syst. Conch.-Cab. ed. 2, 
Limneeiden, p. 88, t. 12. figg. 7-9°. 
Hab. Nort America: San Francisco (P. Carpenter *); Petaluma, N. of San Francisco 
(A. Gould 8), 
N.W. Mexico: Mazatlan, not uncommon (Melchers'; Reigen?). 
This species differs from the preceding (P. wyldz) in the deep excavation of the left 
side; in other respects it resembles young specimens of P. caribeus. According to 
P. Fischer’s figure, said to be taken from a type, P. twmens is very distinct from its 
allies by the deep excavation of the left side of the shell, the species somewhat 
resembling the European P. contortus in this respect; but in the descriptions and 
figures of other authors this character is not so distinctly expressed. P. tumens 
differs, however, from P. tenuis and P. wyldi in the more gradual increase of the 
whorls, this peculiarity giving it the appearance of a not fully grown P. caribeus. 
4, Planorbis caribeeus. (Tab. XXI. figg. 8; 9, 9a, young.) 
Planorbis lentus, Say, Am. Conchology, pt. 6* (the Mexican specimens only). 
Planorbis tumidus, Pfr. in Wiegmann’s Archiv f. Naturg. 1839, p. 354 (sine descr.) *; Dunker, 
in Martini & Chemnitz, Syst. Conch.-Cab. ed. 2, Limneacea, p. 39, t. 7. figg. 10-12 
(1850) *; Binney, Land and Freshw. Shells of N. Am. ii. p. 105, fig. 178° (copy from 
Dunker) ; v. Mart. in Malak. Blatt. xii, p. 54 (1865) °; Strebel, Beitr. Mex. Land- und 
Siissw.-Conch. i. p. 40, t. 5. figg. 20, 206°; Fisch. & Crosse, Miss. Scient. Mex., Mollusca, 
ii. p. 66, t. 34. figg. 4, 4.@,b"; Pilsbry, Proc. Acad. Phil. 1891, p. 322°. 
Planorbis glabratus (Say), Haldeman, Monogr. Limniades, vii. p. 12, t. 2. figg. 1, 3 (specimen 
from Mexico) *. . 
Planorbis caribeus, @’Orbigny, in Ramon de la Sagra’s Hist. fis. polit. y nat. de Cuba, Moluscos, 
p. 108, t. 18. figg. 17-19 (1845?) *°; Clessin, in Martini & Chemnitz, Syst. Conch.-Cab., 
Limneiden, p. 156" *; Arango, Contrib. a la fauna malac. de Cuba, p. 186 (1878) ”; 
Pilsbry, Proc. Acad. Phil. 1891, p. 3822”. 
* The quoted fig. 5, t. 22, is a copy of d’Orbigny’s P. terverianus, not of his P. caribeus, as correctly stated 
49* 
in the explanation of the plates. 
