MAZATLAN tJNIVALVES 291 



+ Calyptrsea (Calypeopsis) quiriquina, Less., B. M. Cat. D'Orb. 



Moll. p. 47, no. 407.— ( = C. Byronensis, Gray in B. M.) 

 + Calyptrsea (Calypeopsis) rugosa, pars solum, B. M. Cat. 



Ubrb. Moll. p. 47, no. 408 ; syn. plur. excl. 



Comp. C. (Calypeopsis) radiata, Brod. Proe. Zool. Soc. 1834., 

 p. 36 :— Trans. Zool. Soc. vol. i. p. 198, no. 6, pi. 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, Lesh. 1836, An. s. 

 Vert. vol. vii. p. 628, no. ll. = Galerus.) 



It is not surprising that tliis beautiful species lias been 

 described under sucb 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 : C. tenuis, the smooth, white, streaked form : 

 C. hispida, the young state of the white shell, with small 

 spines ; C. maculata (non Quoy), 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 coai'se 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 Desk, (not Less.) and in 

 part of D'Orb. These shells are always conical and Hipponi- 

 coid ; which is accounted for by their growing on a narrow 

 base, either on small pebbles, or attached to each other. On 



