CLASS I. CRUSTACEA. 95 



and unequal : tail broad ; the intermediate lamella elongate-trian- 

 gular. 



Sp. 1. Ax. Stin/7ichus. Rostrum margined, the middle carinated: thorax be- 

 hind the rostrum, with two elevated abbreviated lines notched behind. 



A.xius Stirynchus. Ixach, Trans. Linn. Sue. xi. 343. — Supp. to Encycl. 

 Brit. i. ho.—Mul. Foiloph. Brit. tub. 33. 



Inhabits the British sea. 



Stirps 2. Exterior lamella of the tail bipartite: external aidenrKB with a 

 spine-shaped squaine at the first joint of the peduncle: anterior pair 

 c>f legs didactyle. 



* Fj^es subglohose, not thicker than their peduncles. 

 The coxae of the third pair of legs of the female, of the fifth pair 

 of the male, perforated. These perforations are for the passage of 

 the semen and of the eggs ; and although placed differently in other 

 genera, yet they serve the same functions. 



Genus 26. ASTACUS. LeadCs MSS. 



Abdomen with the sides of its segments obtuse : middle tail lamella com- 

 posed of one piece. 



Sp. 1. Ast. Gammarus. Rostrum on each side with four teeth, and with 

 one on each side of its base. 



Cancer Gammarus. Linn. St/st. Nat. i. 1050. As tacus Gammarus. Pe7m. 

 Brit. Zool. iv. 9. pi. 10. Astacus marirms. Fair. Svpp. Ent. Si/sf. 400. 

 Latr. Gen. Crust, et bisect, i. 31. Astacus Gammarus. Leach, Edin. En- 

 cycl. \\\. 398. — Treats. Linn.Soc.M. 344. — Supp. to Encycl. Brit.'i. 420. 

 This species, which is the common lobster of our markets, inhabits 

 deep clear water at the foot of rocks which hang over the sea. They 

 breed during the early summer months, and are very prolific, Baxter 

 having counted no less than 12,444 eggs under the abdomen. In 

 warm weather they are very active; they have the power of spring- 

 ing backward in the water to a most astonishing distance into their 

 holes in the rocks, as has been frequently observed by naturalists of 

 credit. Their food consists oi' dead animal matter, and, it is said, also 

 of sea-weed. The female is stated to deposit her eggs in the sand, but 

 the voung state is not known. 



The common lobster inhabits the European ocean. It is found in 

 verv sreat abundance in the North of Scotland; but is nuich more 

 common on the coast of Norway, from whence the London markets 

 are for the most part supplied. 



Genus 27. POTAMOBIUS. LeacKs MSS. 



Abdomen with the sides of its segments sharp : middle tail lamella bi- 

 partite. 



Sp. 1. Fot.fluviatilis. Rostrurti laterally dentated, tlie base with one 

 tooth on each side. 



Cancer Astacus. Liyin. Syst. Nat. 1. 1051. Astacus astacus. Penn. 



