MAZATLAN BIVALVES 



Tablet 273 contains 7 sp. of various ages, biradiate. 274, 2 

 do. gibbous. 275, 2 do. uniform dirk brown. 276, 1 do. trans- 

 verse, very dark brown. 277, 6 do. and 2 valves, rather dark, 

 not biradiate. 278, 6 do. light gray. 279, 3 do. very light, 

 faint rays, young shell speckled. 280, 2 do. greenish tinge. 

 281, 1 do. purplish. 282, 4 do. concentrically banded with 

 reddish. 283, 4 do. and a young valve, spotted, form like D. 

 iiiaculata. 



!-- 94. DIONE EOSEA, Brod. fy Sow. 



Cytherea rosea, Zool. Journ. iv. 364. Zool. Beech. Toy. Moll. 



p. 151, pi. 43, f. 7. Hani. Descr. Cat. p. 104 : Wood's Suppl. 



pi. 9, f. 11. Phil. Abbild. Conch, p. 183, pi. 5, f. 6. Sow. 



TJics. Conch, p. 632, p. 132, f. 108. 

 Dione rosea, Desk. B. M. Cat. Yen. p. 77, no. 71. 

 Cytherea lepida, Chenu, Conch. HI. 



Shell as usual, either more or less produced posteriorly, or 

 swollen ventrally ; but in all varieties known from D. lupinaria 

 1. by the non- development of spines, which alone might be 

 accidental j 2. by the shape, which is much natter, and gener- 

 ally more produced ventrally ; 3. by the colour, in which pink- 

 ish brown rather than purple predominates, being uniform 

 over the whole shell ; a white streak going along the line of 

 spines without purple at the bases, and a brownish instead of 

 purple patch covering the lunulax portion ; 4. by the anterior 

 larninse, which instead of being close together, are only raised 

 here and there, generally at intervals of 4 or 5 ; 5. by the 

 longer ligament, which is enclosed by a finer ridge, scarcely 

 conspicuous in one valve ; 6. by the absence of the line mark- 

 ing the second row of spines and angulating the posterior 

 margin ; 7. by the teeth which are less raised, more spreading. 

 The colour within is white with diffused violet, no predominant 

 at the hinge. Extremely rarely there is an attempt at the 

 formation of a knob or two where the second row should be, 

 but never a marking line. The concentric ridges are fine, 

 nearly equal, and rarely evanescent ventrally. The ridge which 

 bears the raised lamina does not necessarily bear the raised 

 knobs. The ridges sometimes bifurcate, but are generally more 

 parallel to the margin than in D. lupinaria. I have examined 

 above 500 specimens, in which I believe the above characters 

 are constant. A large number of them are pierced by preda- 

 cious gasteropods. 



