430 



CRUSTACEOLOGY. 



Appendix, bit of the eye without any fissure behind ; eyes not 

 — -y— ' thicker than their peduncles. 



The species of these genera have already been given 

 in the early part of this article, under the generic title 



of PoRTUNUS. 



The genus Cancer, too, admits of several very im- 

 portant divisions, but three genera only have hitherto 

 been.formed, viz. Cancer, Xantiio, and Atelecyclus. 

 Genus I. Cancer. Shell bi-oad, the anterior mar- 

 gin gradually bent into a semi-elliptic form, the ends 

 gradually converging into an angle behind, the apex 

 truncate and marginate : the external antenna; setace- 

 ous and short, the two first joints largest ; inserted be- 

 twixt the front and internal canthus of the eye : Pe- 

 duncle of the internal antennae somewhat lunate. Se- 

 cond joint of external double palpi, with the internal 

 apex emarginate or notched for the insertion of the 

 palpi : Feet simple, compressed, the hinder ones short- 

 est. Nails somewhat compressed and hairy, the sides 

 with an excavated line, joints naked and somewhat acute. 

 Sp. 1. Pagurus. See p. 39 1 of this article. 

 Genus II. Xantho. Shell as in Cancer, but the 

 hinder edge is only submarginate. External antennae 

 very short, setaceous, the two first joints largest, in- 

 serted at the internal comer of the eye ; peduncle of 

 the internal antennae somewhat linear. Palpi as in 

 Cancer. Feet simple, compressed, hinder ones short- 

 est. Nails compressed, hairy, the sides with an obscure 

 impressed line, points naked, and scarcely acute'. 



Sp. 1 . Incisa. Wrists with two tubercles above ; 

 shell on each side with four obtuse teeth, the intersti- 

 ces notched ; fingers generally black, in some indivi- 

 duals same colour with the shell, which is most fre- 

 quently reddish, or brownish-red. 



Cancer incisus of this article. See p. 391. 

 Obs. 1. Cancer dodone of Herbst seems to be refer- 

 able to this genus, as far as we can judge from his 

 plate : it differs in having only three obtuse teeth on 

 each side of the shell. 



Obs. 2. Cancer denticulalus, Hirtellus and Spinifrons, 

 seem also to form distinct genera, but the characters 

 have not yet been developed. 



Genus III. Atelecyclus. The characters have not 

 yet been completely developed ; it is readily distinguish- 

 ed from any other genus by the form of its shell, which 

 is almost continued from the front to the hinder edge 

 into a circle, which is however interrupted in that part, 

 forming altogether an imperfect or interrupted circle. 

 The antennae, too, are as long as the shell. 



Sp. 1 . Septemdentatus. With seven distinct teeth on 

 the sides of the shell, and some intermediate small ones. 

 Cancer lappa septemdentatus, Montagu. 

 First discovered by Montagu on the S. coast of Devon, 

 and described by him in die 1 1 th vol. of the Lin. Trans. 

 It has since been found by Mr Cranch of Kingsbridge 

 to be very common in the Plymouth Sound. Dr Leach 

 received the young of the female from the Bell Rock, 

 sent him by Mr Stevenson. The full grown female 

 has never yet occurred. 



Cancer undecemdentatus of Herbst, tab. 10. fig. 60. 

 seems to belong to this genus. It inhabits America. 



The genus Ocypode Dr Leach has also found it ne- 

 cessary to divide into the following genera. 



* Shell rhomboidal, inclining to square ; peduncle of 

 the eyes reaching the anterior external angles of 

 the shell. 

 Genus I. Ocypode. Peduncle extending beyond 

 the eyes ; anterior feet very unequal. 



Genus II. Uca. Peduncle not extending beyond 

 the iCJWB ; the interior fiwt very unequal. 



Genus III. Goneplax. Peduncle not extending be- Appendix, 

 yond the eyes ; anterior feet equal. ' ■' \T mm ^ 



** Shell truncate-heart-shaped ; peduncle of the eyes 

 much shorter than the anterior external angles 

 of the shell. 



Genus IV. Gecarcinus. 



To the genus Ocypode, O. ceratoplhalmus of this 

 article are referable. To Uca, Cancer nca of Shaw's 

 Nat. Miscellany, plate 588, belongs ; the species to be 

 named Una. To Goneplax, 0. Angulata of this ar- 

 ticle, which should be named G. bispinosa, is the proto- 

 type. To Gecarcinus, 0. ruricola and cordata of this 

 article are the only species we know to belong to it. 



Gen. Grapsus. To this genus Cancer minutus of 

 Linne is referable. 



Gen. Pinnotheres. 



Sp. 1. Pisnm. (Female.) Shell orbicular, soft, very 

 smooth, with the front somewhat arcuate and entire; 

 hands oblong, the under part a line of cilia?, as are the 

 upper parts of the thighs of the other legs ; thumb 

 somewhat arcuate ; abdomen very broad, the sides of 

 the segments arcuate, the fifth segment broader ; the 

 last segment narrower than the preceding ; the apex 

 broadly notched. 



Cancer pisum, Pennant, Fabricius, Linne. 



Pinnotheres pisum, Latreille, Leach, Mem. Wern. Soc. 

 vol. ii. Mai. Brit. Pinnotheres, tab. A. 



Inhabits the shells of mussels and oysters ; male un- 

 known. 



Sp. 2. Mytili. (Female.) Shell orbicular, inclining 

 to quadrate, soft, very smooth, the sides behind dilated; 

 front strait, obscurely, somewhat notched; hands oblong; 

 under parts, with the upper part of the thighs of the other 

 legs, having a ciliated line ; thumb somewhat arcuate ; 

 abdomen very broad, the segments at their sides somewhat 

 arcuate ; hinder edge of the third and following joints 

 notched in the middle ; fifth segment broader, the last 

 narrower than the preceding. 



P. Mytili. Leach, Mem. Wern. Soc. vol. ii. Malacos- 

 tracaBritannica. Pinnotheres, tab. A. Male unknown. 



This interesting species was discovered by a most 

 zealous and enlightened collector, Mr Cranch, in Mytilus 

 modiolus, from the Kingsbridge estuary, dredged from 

 the oyster bed near Gerston Point. 



Sp. 3. Mytilorum. (Female.) Shell ovate-orbicular, 

 anteriorly somewhat narrower, convex very smooth, 

 somewhat solid; front produced entire, scarcely some- 

 what arcuate; sides in each side behind, with two 

 oblique impressed lines running together behind ; hands 

 somewhat oval, beneath, with the upper part of the 

 thighs with a ciliated line ; fingers arcuate ; abdomen 

 somewhat narrow, the segments with their sides some- 

 what arcuate, the last narrower than the preceding, the 

 apex somewhat acuminate, rounded at the extreme 

 point, and entire. 



Cancer mytilorum albus of Herbst. 



Piimotheres mytilorum of Latreille. Leach, Mem. 

 Wern. Soc. vol. ii. Mai. Brit. Pinnotheres, tab. A. 



A single specimen of this species was taken by Dr 

 Leach from Mytilus modiolus, dredged at Newhaven in 

 the Frith of Forth, who, for a long time, considered it 

 as the young of P. Pisum. Male unknown. 



Sp. 4. Varians. (Male.) Shell ovate-orbicular, ante- 

 riorly somewhat narrower, convex very smooth, and so- 

 lid ; front produced, arcuate, and entire ; hands ovate, 

 -beneath with two lines of cilia; ; fingers much arcuated; 

 thighs above and below with a line of cilice ; and sides 

 of the abdomen broadly notched, the last joint abruptly 

 narrower than the preceding, the apex narrower, round- 

 ed, and entire. 



