THIA. CRUSTACEA. 153 



P. corrugatus, Bosc. Shell transversely wrinkled and granulated, 

 with five teeth on each side anteriorly ; claws with a spine on 

 the first and second joint ; forceps serrated ; last pair of legs ovate 

 at the termination, and pointed ; colour red. Inhabits European 

 seas. B. Penn. Brit. Zool. iv. pi. 5, fig. 1. 



P. marmoreus, Leach. Shell convex,, obsoletely and slightly gra- 

 nulated, with five nearly equal teeth on each side ; front with 

 three rounded teeth ; hands smooth, with one tooth above ; co- 

 lour brown, varied with whitish stains. 1^ inch long. Inhabits 

 coasts of England. Malac. Podop/i. Brit. pi. 8. 



Gen. 18. THIA, Leach. Cancer, Herbst. 

 External antennae longer than the body ; anterior legs of the 

 male a little longer than the body, with the head compressed ; 

 other legs with the tarsi half the length of the tibiae, and 

 acute, flexuous, longitudinally sulcated claws ; shell somewhat 

 circular, the sides converging into an angle behind ; eyes 

 very small, scarcely prominent. 



T. polita, Leach. Shell convex, polished, dotted in some places, 

 and the front entire and arcuate ; four obscure folds on each 

 side. Lm. Trans, xi. 312. 



Gen. 19. PORTUMNUS, Leach. Platyonichus, Lat. 

 Eyes not thicker than their peduncles, and the orbits entire ; 

 anterior pair of legs equal, with the forceps long ; the others 

 with compressed claws, dilated internally towards their base ; 

 the fifth pair terminated by a flattened foliaceous claw ; shell 

 with the transverse and longitudinal diameters the same. 



P. variegatus, Leach. (C. latipes, Pen.) Shell obscurely granu- 

 lated on each side, with five teeth, the second and third some- 

 what obsolete ; front with three teeth ; wrists with one internal 

 tooth. Inhabits European seas. B. Penn. Brit. Zool. iv. pi. 1, 

 fig. 4. (Female.) 



P. Henslowii, Lat. (Polybius, Leach.) Shell slightly granulat- 

 ed, with five broad teeth on its anterior sides; front trilobed, 

 with the middle lobe more pointed than the lateral ones. Inha- 

 bits coast of Devonshire. Malac. Brit. pi. 9. 



FAMILY III. ORBICULATA. 



Shell orbicular or ovoid, narrower before than behind, and ge- 

 nerally with two depressions or furrows ; third joint of the 

 exterior feet-jaws triangular. 



Gen. 20. MATUTA, Lat. 



Exterior antennae much smaller than the intermediate ones ; 

 eyes separated by a trilobed projection in front, on short sub- 

 conical peduncles ; shell suborbicular, depressed, with the 

 sides dilated into a very strong spine ; forceps equal, thick, 



