MAZATLAN BIVALVES 59 



ffab. Sta. Barbara ; Nuttall, Col. Jewett&&n Diego ; Lieut. 

 Green. Mazatlan ; Lieut. Green. (Grould ms.) ?? do ; from 

 shell washings ; Lpool Col. 



_(- 87. TEIGONA PLANULATA, Brod. fy Soiv. 



Cytherea planulata, Zool. Journ. vol. v. p. 48. Sow. Gen. f. 2. 

 Rve. Conch. Syst. vol. i. p. 94, pi. 69, f. 2. Hani. Descr. Cat. 

 p. 105. Zool. Beech. Voy. p. 151, pi. 43, f. 6. Sow. I7ies. 

 Conch, p. 618, no. 20, pi. 127, f. 13. 



Venus planulata, B. M. Cat. DOrb. Moll. p. 66, no, 587. 

 Trigona planulata, Gray Cat. Cytli. Anal. vol. viii. p. 304. 



Desk. B. M. Cat. Ven. p. 48, no. 8. 

 + Var. suffusa, Sow. Proc. Zool. Soc. 1.835, p. 46. 

 + Cytherea undulata, Sow. Thes. Conch, p. 618, no. 21, pi. 127, 



f. 12. (Trigona u.) Desk. B. M. Cat. Ven. p. 48. no. 9. 

 = Donax Lessoni, Desk. JEnc. Meth< vers. t. 2. p. 99. 

 (teste Desk.) Cytherea mactroides, Lam. (non Born nee Sow.) 

 An. s. Vert. vol. vi. p. 307, no. 27.Deless. Rec. de Coq. pi. 8, 

 f. Z.^Hanl. Descr. Cat. p. 99 : Wood Suppl. pi. 13, f. 17. 

 The very illustrioiis 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. fy 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 undulatse are if anything thinner than the planulatse. 

 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 j 

 anterior lateral much prolonged. The W. African analogue is 

 T. bicolor, Hani. 



Typical form measures long. 2', lot. 2*3, alt. 1*. 

 Var. undulata 1'78, 2'2, '88. 



Hob. Panama, Cuming. Chili ; Coquimbo ; TfOMgny. 

 Found abundantly near Mazatlan ; Lieut. Belcher. Maz- 

 atlan ; not common ; Lpool Col. Var. suffusa ; Salango, 

 sandy mud, 9 fm. Cuming. Var. undulata, do. Cuming. 



