GENUS TETRACLITA. 321 



Zoologie, 1831, Tab. 39 ; and Guerin, Iconographie du 

 Regne Animal, Mollusques, Tab. 38, fig. 4, but here by a 

 misprint called A. spinulosa) ; it is utterly impossible to 

 recognise the species of this genus from such materials. 



3. Genus — Tetraclita. PI. 10, 11. 



Tetraclita. Schumacher. Essai d'un Nouveau Syst., &c, 1817. 

 Conia. Leach. Journal de Physique, torn. 85, 1817.* 

 Asemus. Ranzani. Memoire di Storia Naturale, 1820.f 

 Polytrema. De Ferussac. Diet. Classique d'Histoire Naturelle, 



1822. 

 Lepas. Gmelin. Systema Naturae, 1789. 

 Balanus. Bruguiere. Encyclop. Method., 1789. 

 — Lamarck. Aniinaux sans Vertebres, 1818. 



Compartments four, sometimes externally calcified together : 

 parietes permeated by pores, generally forming several rows. 

 Basis flat, irregular, calcareous , or membranous. 



Hab. — Throughout the tropical and warmer temperate seas. 



General Appeara?ice. — The shell is conical, more or 

 less depressed, and very rarely, even when growing in 

 crowded groups, becomes cylindrical or elongated. The 

 orifice is seldom large, generally diamond-shaped or oval. 

 The colour is either nearly white or purple, occasionally 

 even inky black, or very dark green, and sometimes of a 

 pale pink peach-blossom. The surface is sometimes smooth, 

 but more commonly longitudinally ribbed; the outer lamina 

 of shell is very often wholly corroded: away, excepting close to 

 the basis, leaving the solidly upfilled parietal tubes exposed: 

 these give the shell a striated appearance, or they appear 

 like flattened tapering points adpressed to its surface (PI. 10, 



* Prom a note by the Editor, it appears that Schumacher's essay appeared 

 before the number of the Journal containing Leach's paper, so that Schumacher's 

 name must be adopted. 



f I have not seen a complete copy of this work, and give the title from a 

 catalogue ; the running heading of the part containing the Cirripedia, is 

 " Opuscoli Scientifici." 



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