POLYMESODA. 545 
Hab. British Honpuras : Belize (Prime®). 
Crntrau Nicaracua: Lake of Nicaragua !. 
W. Nicaragua: Greytown (San Juan del Norte), with Neritina virginea, in brackish- 
water pools, burrowing to a depth of one or two inches in the sandy bottom 
(Tate). 
The figures given by Clessin 4 and Fischer and Crosse (fig. 2)7 do not agree very 
well with the two specimens from Nicaragua in Dunker’s collection shown on our 
Plate (probably given by Philippi); the former is too much rounded, especially in the 
fore part, the latter is too much produced in the fore part and has a distinct angular 
ridge limiting the posterior area; moreover, in these figures the pallial sinus is too 
horizontal. Fischer and Crosse’s fig. 2 a, dorsal view, on the contrary, agrees very 
well with the above-mentioned Nicaraguan examples. 
Dr. Morch’s unnamed species ® appears to be very like the specimens in Dunker’s 
collection. Obsolete radial furrows inside the ventral margin are more or less 
distinctly expressed in all examples of Polymesoda; they are not, therefore, of specific 
importance, 
3. Polymesoda radiata. 
Cyrenu radiata, Hanley, P. Z.S. 1844, p. 159"; Deshayes, Cat. Conchifera Brit. Mus. ii. p. 254° ; 
Prime, Monogr. Am. Corbiculade, p. 13, fig. 7°; Clessin, in Martini & Chemnitz, Syst. 
Conch.-Cab. ed. 2, Cycladea, p. 118, t. 22. figg. 1, 2°. 
? Cyrena radiata, Sowerby, in Reeve’s Conch. Icon. xx., Cyrena, t. 13. fig. 47° [nec Cyrena radiata, 
Parreyss, Philippi (1846) (Corbicula)]. 
Cyrena nicaraguana, var. 8. radiata, Fisch. & Crosse, Miss. Scient. Mex., Moll. ii. pp. 540, 541°. 
Differs from the preceding in having some rather broad green rays. Some specimens are more compressed, and 
more intensely violet inside; moreover, the anterior dorsal margin descends a little more deeply and the 
anterior lateral teeth are correspondingly longer than in P. solida. Sculpture and pallial sinus similar. 
a. Long. 42, alt. 40, diam. 30 millim. Vertices in 2 long. 
S30, ,, 38, 4, 29 ©; ” 2 4 
C. 9 42, 99 39, 99 28 39 2 39 . . 
a, b. Specimens in the Berlin Museum; c. Measurements given by Prime *. 
Had. British Honpuras: Belize (Bocourt ®). 
W. Nicaragua: Realejo (Prime *). 
Hanley! merely gives Central America as locality. 
4, Polymesoda placens. (Tab. XLII. figg. 4, 4a, 6, 5, 5a, 6.) 
Cyrena placens, Hanley, P. Z. S. 1844, p. 160°; Catal. Recent Bivalv. p. 352, t. 14, fig. 52°; 
Prime, Monogr. Am. Corbiculade, p. 20° [nec C. placida, Deshayes (1854) ; Sowerby, in 
Reeve’s Conch. Icon., Cyrena, t. 18. fig. 106]. 
Cyrena solida (Phil.), Stoll, Guatemala Reisen und Schilderungen, 1886, p. 472*. 
Triangular, shining, dark brownish-green, with strong, close, regular concentric ridges ; ventral margin more 
BIOL. CENTR.-AMER., Terr. and Fluviat. Mollusca, October 1900. 69 
