66 MAZATLAN BIVALVES 
Tablet 273 contains 7 sp. of various ages, biradiate.—274, 2 
do. gibbous.—275, 2 do. uniform dark 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. 
maculata. 
94. DionE roses, Brod. & Sow. 
Cytherea rosea, Zool. Journ. iv. 364.—Zool. Beech. Voy. Moll. 
p. 151, pl. 43, f. 7—Hanl. Descr. Cat. p. 104: Wood's Suppl. 
pl.9, f. 11.— Pil. Abbild. Conch. p. 183, pl. 5, f. 6.—Sow. 
Thes. Conch. p. 632, p. 132, f. 108. 
Dione rosea, Desh. B. M. Cat. Ven. p. 77, no. 71. 
Cytherea lepida, Chénu, Conch. Ill. 
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 ; 2. by the shape, which is much flatter, 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 lunular portion; 4. by the anterior 
lamine, 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,not 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. 
