CLASS I. CRUSTACEA. 87 



Stalk, one-jointed : anterior pair of legs unequal : ej/CS thick : shell 

 ovate-orbicular, orbiculate-quadrate, or transverse subquadrate. 



All the species of this most interesting genus inhabit the bivalve 

 shells of the acephalous Mollusca, and were supposed by the ancients 

 to be consentaneous inmates with the animal, bound by mutual in- 

 terest. 



Aristotle supposed them to act as sentinels, and believed that they 

 guarded the Pinna (the animal in whose shell they were first observ- 

 ed) from the attacks of its enemies. Rondeletius and some other 

 naturalists held the same opinion. 

 Sp. 1. Pin. Cranchii. Shell orbiculate-subquadrate, soft, very smooth,with 

 the sides dilated behind : front ^straight, obscurely subemarginate : 

 hands oblong below, and the thighs above with a ciliated line: 

 thumb subarcuate : abdomen very broad ; the sides of the segment 

 arcuate ; the second and following ones distinctly notched ; the fifth 

 segment somewhat broader ; the last narrower than the preceding 

 segment. Female. 

 Pinnoteres Cranchii. Leach, Malacost. Podoph. Brit. tab. 14. Jig. 4. 5. 



The male of this species, which was discovered by Mr. J. Cranch, 

 whose name it bears, is unknown. It is distinguished from P. Pisum 

 (the common species) by the form of the front of the shell, which is 

 straight, and slightly notched ; by the dilated hinder part of the shell, 

 and by the abdomen, all the joints of which, excepting the first, are 

 distinctly notched behind. 



** Shell quadrate. Ei/eswith a long peduncle. 



Genus 10. GONOPLAX. Leach. Ocypoda. Bosc. 

 E^es terminating their peduncle : anterior pair of legs equal ; of the 



male very long; of the female twice the length of the body : antenna 



half the length of the body, inserted at the internal canthus of the 



eyes. 

 The animals of this genus inhabit the ocean, preferring such parts 



as have a slimy bottom. They barrow laterally in the clay or slime, 



making two entrances to their hole; entering by one and going out 



by the other. 

 Sp. 1. Gon. bispinosa. Shell on each side with two spines : arms above, 



and wrists internally, with one spine. 

 Cancer angulatus. Penn. Brit. Zool. iv. t.o.f. 10. Fabr. Siippl. Entom. 



Sj/st. 341. Ocypoda angulata. Bosc, Hist. Nat. des Crust. 1. 198. 



(ionoplax bispinosa. Leach, Trans. Linn. Soc. xi. 323. — Edin. Enci/cl. 



— Sirpp. to Enci/vl. Brit. — Mai. Podoph. Brit. tab. 13. 

 Inhabits the British sea. It is not uncommon at Salcombe and in 



Plymouth sound; and likewise occurs at Weymouth, and at Red 



Wharf in Anirlesea. . 



