DECAPODA MACRURA. 477 



Bobretzky (prawns and cray-fish) and Reichenbach (cray-fish) have 

 yielded important results. The segmentation seems (in all cases?) 

 to be superficial (centrolecithal), that is, to be confined to the 

 peripheral yolk (formative yolk). This divides successively into two, 

 four, eight, and an increasing number of segmentation cells, while 

 the central granular food yolk, which is rich in oil globules, remains 

 unsegmented. The young of Astactw, when hatched, resemble the 

 adult animal, excepting that the caudal fin is still rudimentary. 



I. MACRURA. 



The abdomen is strongly developed and is at least as long as the 

 anterior part of the body \ there are four or five pairs of abdominal 

 feet and a broad, well-developed caudal fin. The antennules bear 

 two or three flagella, the antennae have one simple nagellum and 

 frequently bear a scale at the base. The maxillipeds of the third 

 pair are long and pediform and do not completely cover the pre- 

 ceding ones. The Zocea larva, when hatched, is elongated and has 

 usually three pair of biramous feet. 



Fam. Carididae. Prawns. Body laterally compressed, with a thin shell, which 

 is often provided with a median ridge and prolonged into a saw-like frontal 

 process. The posterior (external) antennae are inserted beneath the anterior 

 (internal) and have a large scale projecting over the stalk. The long and 

 slender anterior pairs of ambulatory legs frequently end in chelae. They live in 

 shoals near the coast. Some genera (Penceus) possess a rudimentary swimming 

 ramus. Palcsmon squilla L., Crangon vulgaris Fabr., Pontonia tyrrliena Risso. 

 lives between the shells of bivalves. Sergcstes atlanticiis Edw. 



Fam. Astacidae. Tolerably large, usually with a hard shell. The cephalo- 

 thorax is slightly compressed, the abdomen flattened. The antennas are attached 

 near the antennules, and bear a small or quite reduced scale at their base. The 

 first pair of ambulatory feet ends with large chelae, as do in many cases the 

 weaker and smaller second and third pairs. Some soft -skinned forms bury 

 themselves in the mud or sand. Astacus fluviatilis Rond., Crayfish. Homarns 

 vulgaris Bel., Lobster. JVephrops norwegicus L., Grcbia Leach., Thalassina 

 Latr., Callianaxsa subtcrranea Mont., buries itself in sand on the sea-shore. 



Fam. Loricata. With very hard, rough armour, and large broad abdomen 

 The antennules end with two short flagella ; all five pairs of ambulatory feet 

 with simple claws. The larvae are described as species of Phyllosoma. 

 Palinurus qvadriccrnis Latr. ScyHarus latus Latr. 



Fam. Galatheidao. With broad, rather large abdomen, and well-developed 

 caudal fin. The first pair of legs is chelate, the last is weak and reduced. 

 GalatJica strigosa L. 



Fam. Hippidae. Cephalo-thoracic shield long ; end of the abdomen curved. 

 The first pair of legs usually with a finger-shaped terminal joint ; the last is 



Kiew, 1873, compare H. Reichenbach, " Die Embryonalanlage und erste Ent- 

 wickelung des Flusskrcbses," Zeitschr.fur wiss. Zool., Tom XXIX., 1877. 



