DECAPODA MACRUHA. 477 



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

 yielded important results. Tlie 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 

 unsegrnented. The young of Astacus, when hatched, resemble the 

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



I. MACRUEA. 



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 aiitennules bear 

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

 frecj[uently 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. Carid.id.ae. 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) antennas 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 chclre. They live in 

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

 ramus. Palcemon squilla L., Crangon vulgar is Fabr., Pontonia tyrrltena Risso. 

 lives between the shells of bivalves. Sergcstcs atlanticus Edw. 



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

 thorax is slightly compressed, the abdomen flattened. The antenna 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. Homarun 

 vulgar is Bel., Lobster. Neplirops normcgicus L., Gclui Leach., Thalassina 

 Latr., CiillianiiMit, subterranea Mont., buries itself in sand on the sea-shore. 



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

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

 with simple claws. The larra are described as species of Phyllosaiiiu. 

 Palinurus quadriccrnis Latr. Sci/Uarus latus Latr. 



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

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

 Galatlica strlgosa 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 erstc Ent- 

 wickelung des Flusskrcbses," Zritschr. fur wins. Zool. t Tom XXIX., 1877. 



