Sub-Glass 2. Malacostraca. Order 5. Amphipoda. 219 



feet prehensile. Marine and fresh, water : G. locusta, common on all European 

 coasts ; the nearly allied G. flweiaUUs frequent in fresh water ; the blind 

 Q. (Niphargus) puteanus in springs. 



2. Many genera of the Hyperidx are found in the open sea ; these are 

 transparent Amphipods, with colossal eyes ; some of them Ure in jeUy fish and 

 other transparent forms ; in the common Aurelia, for instance, the species 

 Hyperia galba is often found. 



3. The genus Caprella, Skeleton Shrimp, characterised by nadimentary 

 abdomen (reduced to a blunt process, and destitute of appendages), and the 

 possession of only six free thoracic segments (two of them being fused with the 

 head). The body is long and thin, almost filiform ; the second and third pairs 

 of thoracic Umbs form chelae (the first pair of these is smaU, the other large) ; of 

 the fourth and fifth pairs only the basal joint and the gill lamella are present 

 (gills ai-e absent from all the other appendages), the sixth to the eighth are true 

 ambulatory legs. Caprella is marine, and wanders about slowly over seaweeds 

 and colonial animals. Cyamus is nearly allied ; its six free thoracic segments 

 are each produced on either side into a long process bearing a leg at the tip, so 

 that the body is flat and isopodan in appearance; in other respects very like 

 Caprella. Parasitic on the skin of the Whale, devouring its thick epidermis. 



Order 6. Dccapoda. 



The ■well-developed carapace is fused with all eight thoracic 

 segments dorsally, but the lateral parts are free (branchiostegites), 

 and between them and the trunk there is, on either side, a roomy 

 cavity, the branchial chamber. The eyes are placed 

 on movable stalks, the antennules have as a rule (excepting 

 in Crabs) a lamellate, unjointed exopod. Of the thoracic legs 

 (.see Fig. 170, p. 208), the three anterior pairs are modified to 

 form maxillipeds; the first pair is much flattened, as are also the 

 first and second maxillae ; the other two pairs differ but little from 

 the rest of the thoracic feet, but are usually much shorter. The 

 remaining five pairs of thoracic appendages are known as ambu- 

 latory legs. They are essentially walking legs, but one or 

 more pairs (usually the front pair) are generally modified to form 

 claws (chelae), the penultimate joint being elongated into a strong 

 process, against which the terminal joint bites. Such are used either 

 exclusively, or in addition to their normal function, as prehensile 

 organs. The maxillipeds have, as a rule, a very well-developed, 

 slender exopod, which is almost always absent from the ambula- 

 tory legs ; an e p i p o d may be present on both sets of thoracic 

 limbs, and always projects into the gill-cavity. The gills arise 

 from the epipods, from the sides of the thorax, and from the arthro- 

 dial membranes, between the thorax and its appendages. Each 

 consists of an axis with two series of lamellee, or with a large 

 number of filaments ; of such gills there are from five to twenty odd 

 on each side. They are situate in the branchial cavity, into which 

 water usually enters at the base of the thoracic feet, flows over the 



