MAZATLAN UNIVALVES 291 
+ Calyptrea (Calypeopsis) quiriquina, Less., B. M. Cat. D’ Orb. 
Moil. p. 47, no. 407.—(=C. Byronensis, Gray in B. MM.) 
+Calyptrea (Calypeopsis) rugosa, pars solum, B. M. Cat. 
D’ Orb. Moll. p. 47, no. 408; syn. plur. excl. 
Comp. C. (Calypeopsis) radiata, Brod. Proc. Zool. Soc. 1834, 
p. 36:—Trans. Zool. Soc. vol. i. p. 198, no. 6, pl. 27, f. 6— 
Lam. An. s. Vert. vol. vii. p. 635, no. 31.—C. B. Ad. Pan. 
Shells, p. 223, no. 339.—(Non C. radiata, Desh. 1836, An. s. 
Vert. vol. vii. p. 628, no. 11.=Galerus.) 
It is not surprising that this beautiful species has been 
described under such a variety of names, as the differences 
between individuals are patent at first sight; their affinities 
only after a careful examination of a large multitude of speci- 
mens. And yet, though it would be most difficult to frame a 
description that should include the whole and exclude neigh- 
bouring species, the general habit of growth is such that it is 
not difficult to recognize. The Mazatlan specimens alone 
prove the C. tenuis, C. hispida and C. maculata, of Brod. to be 
merely forms of growth of C. spinosa, Sow., which pass into 
one another by such gradual steps that they cannot be separ- 
ated even as varieties. The supposed differences observable 
in the Cumingian types are as follows. C. imbricata, olim (one 
of two shells differing specifically from each other, and each 
claiming the name of Brod. to the confusion of students ; an 
error now corrected) was the young state, before the cup is 
entirely formed: ©. tenuis, the smooth, white, streaked form : 
C. hispida, the young state of the white shell, with small 
spines ; C. maculata (non Quwoy), a rather older stage, smooth 
and spotted. The C. radiata, in most respects agreeing with 
C. spinosa, differs in the remarkable flattening of the cup, and 
in its greater separation from the margin. 
‘The C. quiriquina of Lesson and D’Orbigny, (which is the 
C. Byronensis, Gray ms.) belongs to a Southern type which 
may be distinct ; though it has characters enough in common 
to make it not impossible that it is only a coarse variety. It 
is characterized by a more solid texture, light reddish brown 
colour, entire absence of spines, and a less angulated cup. To 
this form is referable, as an aberrant, variety, the C. lignaria 
of Brod., which is the C. rugosa of Desh. (not Less.) and in 
part of D’Orb. These shells are always conical and Hipponi- 
eoid ; which is accounted for by their growing on a narrow 
base, either on small pebbles, or attached to each other. On 
