NEOCORBICULA.—SPH ERIUM. dol 
Deshayes!2 states that it is found in the rivers of Central America, without 
mentioning any definite locality ; but in his collection the specimens are labelled Rio 
de la Plata, according to Fischer and Crosse ¢, 
Prime‘ states that-N. convera differs from all other species of the genus by its 
globular shape; externally it somewhat resembles the young of Cyrena mexicana. Is 
it possible that in very young examples of Polymesoda the lateral teeth also are 
transversely furrowed 2 
SPHARIUM. 
Spherium, Scopoli, Introd. Hist. Nat. p. 397 (1777) [re-introduced by Gray, P. Z.S. 1847, p. 184]. 
Cyclas, Bruguiére, Encycl. Méth., Vers, i. p. 536 (1792) [restricted by C. Pfeiffer, Naturg. Deutsch. 
Land- und Siissw.-Moll. i. p. 119 (1821)]. 
Shell nearly globular, rounded before and behind, summits not far from the middle 
of the length ; two cardinal teeth in the left valve, one or two in the right, anterior 
and posterior lateral teeth present, somewhat elongated. No pallial sinus. Two 
siphons of unequal length, united at the base. 
Generally distributed, chiefly in the temperate zones, in stagnant water ; viviparous. 
1, Spherium triangulare. 
Cyclas triangularis, Say, in New Harmony Disseminator of Useful Knowledge, 1829, p. 356". 
Spherium triungulare, Prime, Monogr. Am. Corbiculade, p. 36, fig. 28°; Clessin, in Martini & 
Chemnitz, Syst. Conch.-Cab. ed. 2, Cycladeen, p. 99, t. 12. fig. 8 (not very exactly copied 
from Prime)’; Fisch. & Crosse, Miss. Scient. Mex., Moll. i. p. 651°. . 
Ovate-orbicular, nearly equilateral, summits prominent, fore part produced and somewhat narrowed, hinder 
part shortly rounded. 
Long. 123-138, alt. 10-104, diam. 3 millim. Vertices in about 3 long. 
Hab. Mexico (Say). 
2. Spherium subtransversum. 
Spherium subtransversum, Prime, P. Z. 8S. 1860, p. 322°; Monogr. Am. Corbiculade, p. 52°; 
Sowerby, in Reeve’s Conch. Icon. xx., Spherium, t. 4. fig. 38°; Fisch. & Crosse, Miss. 
Scient. Mex., Moll. ii. p. 652, t. 69. figg. 5, 5a*. 
Nearly equilateral, rounded before and behind, somewhat shorter before; summits a little prominent, ventral 
margin arcuated. a 
Long. 102-13, alt. 83-10, diam. 6-7 millim. Vertices in 2 long. 
Hab. Cenrrat Mexico: near the town of Mexico (Boucard *). 
E. Mexico: Rio del Digue, near Jalapa (Strebel); Jalapa (Hoge; PF. D. Godman, 
Feb. 1888); Cordova (Hoge). 
S.E. Mexico: Tabasco (coll. Cuming '**). 
