546 MOLLUSCA. 
arcuated before than behind. Inside pale violet or salmon-coloured in the middle, pale violet near the 
margins; pallial sinus diagonally ascending, not very narrow, obtuse at the upper end, yellowish-green. 
a. Long. 44, alt. 38, diam. ? millim. Vertices in 2 long. 
b. ” 43, ” 37, ” 29 ” ” 2 ” 
C. 39 40, 99 33, 9? 42 99 29 2 99 
a, Hanley’s measurements and figure; 6, c. Stoll’ s specimens. 
Hab. Honvvras !-%. 
E. Guatema.a, Livingston, in the Gulf of Honduras (Stol/ +). 
Carpenter (Catal. Mazatlan Shells, p. 114) thinks that this species may be identical 
with C. fontaine?, d’Orb. ; and Prime ® says “ I have reason to believe that P. placens is 
closely allied to C. fontaine.” 
5. Polymesoda triangula. 
Cyrena triangula, von dem Busch, in Philippi’s Abbild. neuer Conch. iii. p. 78, t. 2. fig. 3 (1849) ’; 
Deshayes, Catal. Conchifera Brit. Mus. il. p. 253°; Prime, Monogr. Am. Corbiculade, 
pp. 14, 23°; Clessin, in Martini & Chemnitz, Syst. Conch.-Cab. ed. 2, Cycladeen, p. 112, 
t. 14. fig. 1°; Fisch. & Crosse, Miss. Scient. Mex., Moll. ii. p. 635, t. 70. figg. 6, 6a, 5’. 
Cyrena altilis, A. Gould, Boston Journ. of Nat. Hist. vi. p. 400, t. 16. fig. 5 bis (1852-58) °. 
Cyrena mexicana, var. altilis (A. Gould), Carpenter, P. Z. S. 1856, p. 2027. 
Cyrena mexicana (Brod., Sow.) a very extreme form, Mr. Darbishire’s specim., Carpenter, Cat. 
Mazatlan Shells, p. 116°. 
Almost equilaterally triangular, and nearly as high as long; posterior dorsal margin slightly convex ; ventral 
margin moderately excavated. 
Long. 58-60, alt. 54-56, diam. 30 millim. Vertices in 2—3 long. 
Hab. N.W. Mexico: Mazatlan, in abundance (Reigen’, Jewett °). 
The habitat of the typical specimens! is not known. Clessin4+ mentions also 
“Zampico” as a locality for this species, probably a misprint for Tampico, in 
N.E. Mexico; but I can find no authority for this statement. P. triangula must 
not be confounded with Cyrena triangularis, Metcalfe (1851), from Borneo. 
6. Polymesoda cordata. (Tab. XLII. figg. 7, 7 a, 0.) 
Cyrena cordata (Wiegmann, in Mus. Berol.), v. Mart. Malak. Blatt. xii. p. 69 (1865)*; Fisch. & 
Crosse, Miss. Scient. Mex., Moll. ii. p. 639 ”. 
Near the preceding, but more unequilateral ; the anterior side descending very steeply, the posterior side more 
convex. Dark brown, with close concentric striz ; inside white (bleached ?). Pallial sinus rather narrow 
and long, very oblique. 
Long. 48, ait. 44, diam. 33 millim. Vertices in } long. 
Hab. Mexico: without nearer indication of locality (Deppe !”). 
Deppe collected at Vera Cruz, Jalapa, Mexico city, and Monterey; it cannot, 
therefore, be decided as to which region of Mexico this species belongs. 
UJ _ 
enemnesetostinenen, 
