MAZATLAN BIVALVES 59 
Hab.—Sta. Barbara; Nuttall, Col. Jewett—San Diego; Lieut. 
Green.—Mazatlan ; Lieut. Green. (Gould ms.)—?? do; from 
shell washings ; L’pool Col. 
87. TRIGONA PLANULATA, Brod. & Sow. 
Cytherea planulata, Zool. Jowrn. vol. v. p. 48.—Sow. Gen. f.2.— 
Rve. Conch. Syst. vol. i. p. 94, pl. 69, f.2.—Hanl. Deser. Cat. 
p- 105.—Zool. Beech. Voy. p. 151, pl. 43, f. 6.—Sow. Thes. 
Conch. p. 618, no. 20, pl. 127, f. 13. 
Venus planulata, B. M. Cat. D’ Orb. Moll. p. 66, no, 587. 
Trigona planulata, Gray Cat. Cyth. Anal. yol. viii. p. 304— 
Desh. B. M. Cat. Ven. p. 48, no. 8. 
+ Var. suffusa, Sow. Proc. Zool. Soc. 1835, p. 46. 
+ Cytherea undulata, Sow. Thes. Conch. p. 618, no. 21, pl. 127, 
f. 12.—(Trigona u.) Desh. B. M. Cat. Ven. p. 48. no. 9. 
= Donax Lessoni, Desh. Enc. Méth. vers. t. 2. p. 99. 
=(teste Desh.) Cytherea mactroides, Lam. (non Born nee Sow.) 
An. s. Vert. vol. vi. p. 307, no. 27.—Deless. Rec. de Coq. pl. 8, 
f. 2.—Hanl. Descr. Cat. p.99: Wood Suppl. pl. 13, f. 17. 
The very, illustrious Deshayes in his later works seems much 
more disposed to the multiplication of species than he was in 
his earlier edition of Lamarck. He follows Sow. jun. in divid- 
ing the C. planulata of Brod. & Sow. The C. undulata is 
discriminated by its more equal form, greater solidity, absence 
of posterior gape, distinctness of lunule and style of painting. 
I have not found any one of these characters constant. The 
species varies almost as much as its more swollen congener, 
T. radiata. In form there is a gradual passage between the 
two. The undulate are if anything thinner than the planulate. 
The breaking up of the coloured rays proceeds by insensible 
gradations, and the colouring of the interior varies greatly. 
The gaping is either posterior, or anterior, or both, or some- 
what ventral, or none, just as it happens. The beaks are scarcely 
ever tipped with purple. The painting of the two valves does 
not always correspond. The teeth are very small and angular ; 
anterior lateral much prolonged. The W. African analogue is 
T. bicolor, Hani. 
Typical form measures long.2°, Jat. 2°3, alt. 1°. 
Var. undulata __,, 5p UPS Ta Ow Tle Ray 
Hab.—Panama, Cuming—Chili; Coquimbo; D’ Orbigny.— 
Found abundantly near Mazatlan; Lieut. Belcher —Maz- 
atlan; not common; L’pool Col.—Var. suffusa; Salango, 
sandy mud, 9 fm. Cuming.—Var. undulata, do. Cuming. 
