WILLIAMSON, ON SHELLS OF CRUSTACEA. ^3 



both ill the carapace and in the tail, though less so in the 

 claws ; hut the chief interest lay in the calcified corium, 

 especially at its peripheral portion. On looking at a vertical 

 section, the tubulated structure of this layer was rendered 

 confused and indefinite by some vague radiating elements. 

 On making a horizontal section immediately below the 

 areolar layer, the nature of these radiations became obvious. 

 The entire section was covered with regular hexagonal areolae 

 of exquisite beauty (fig. 14). Each areola consisted of 

 numerous irregular rods, radiating from a solid centre, sub- 

 dividing like the outspread arms of an encrinite, a resemblance 

 which higher magnifiers only rendered more obvious, since 

 each radiating arm then appeared jointed ; but this was an 

 illusion. The whole was but a congeries of botryoidal rods 

 (fig. 15), the result of a concretionary process of growth ; the 

 small tubercles with which each rod was studded being the 

 homologues of those seen in the large calcareous discs of the 

 shrimp. This structure was wholly distinct from the areolated 

 layer of the integument. Between these stellate objects, 

 there occasionally occur solidly calcified portions, often pene- 

 trated by a large vertical canal. 



When a vertical section was decalcified, all these distinc- 

 tive features disappeared. I now only saw a series of parallel 

 chitinous laminae, traversed by undulating vertical tubules ; 

 the line of separation between the areolated layer and the 

 corium being very indistinct. Of these laminae I counted 

 about 60 in a section of the integument of the tail, whilst 

 there were 120 in the claw of the same individual, showing 

 that they are not consentaneously developed in all parts of 

 the animal. On the external surface of the lobster's shell are 

 numerous small depressions ; at the hollow of each of these 

 are the orifices of several vertical tubes which descend through 

 all the subjacent tissues. 



The hard calcified claw of the hermit crab further illustrates 

 some of these points. A vertical section made through one 

 of the numerous superficial tubercles (fig. 16) demonstrates 

 that these latter are the homologues of the white spots on the 

 shell of the common crab. We here see distinctly that the 

 uplifted layers of the corium (d) pass through the areolated 

 structure (b) and are brought into contact with the pellicle (a), 

 whilst the corresponding thickened portion of the latter, here 

 considerably thickened, is penetrated by tubuli or fibres (e) 

 similar to those seen in the homologous portion of the common 

 crab. This close relation of the upraised portions of the 

 corium to the pellicle, and the absence of the areolar layer 

 at such points, is also shown in Hyas araneus, Poriumnus 



