300 ZOOLOGY. 



CLEODORA CUSPIDATUM. 



This is a vitreous shell of extreme delicacy and 

 beauty. It is colourless and transparent,, elegantly 

 grooved on the surface, and so fragile as scarcely to 

 bear the slightest touch. It is pyramidal and nearly 

 triangular in form : its anterior and broader extremity 

 having a broad aperture, while its apex is an acute and 

 slightly-curved point. A long slender spine, or vitreous 

 needle, projects from the margin of the aperture ; and 

 a similar spine is placed on each side of the shell, near 

 its centre. The animal it contains is furnished with 

 two simple branchice, or wings, like Hyalaea. On that 

 part of its body which is lodged in the apex of the 

 shell, there is a small globular pellucid body, resembling 

 a vesicle, and which at night emits a luminous gleam, 

 sufficiently vivid to be visible even when it is opposed 

 to the strong light of a lamp. It is the only instance 

 of a luminous shell-fish I have ever met with ; * nor 

 would the luminosity of this species be of any avail, 

 did not the shell possess a structure so vitreous and 

 transparent. Examples were chiefly captured at night 

 or in the evening. They were obtained in great 

 abundance near the surface of the Pacific, between the 

 Equator and lats. 16 S. and 30 N. 



C. Balantium was more rarely noticed ; and I have 

 not observed that its animal possesses any luminous 

 quality. In structure and general appearance the shell 

 resembles that last described, but is larger and more 

 pyramidal. It has a short curved spine at its apex, 

 and its sides are toothed, or serrated ; but it has no 

 long spines. 



* A second shell-fish, the Pholas dactylus, or Piddock, a British 

 species, is said to shine by night ; but I am not aware that we have any 

 competent authority for its luminous power being a vital attribute, or 

 for the precise manner in which it is displayed. 



