On. the Hkar/cs of the Family Cestraciontidae. 49:> 



Norfolk Broads ; as tlie result T can iitihesitatingly pronounce 

 them to belonp^ to the common species C. lacustris, originally 

 discovered by Allnian in the docks of London and Dublin. 



This is the first record of the genus from Africa. In Lake 

 Qurun the hydroid was found in a variety of positions : on 

 water-weeds, on tamarisk-stumps, and on the under side of 

 rocks and large stones at the water^s edge ; in the latter 

 position, shaded from the light, the colonies reached tbeir 

 greatest development. 



The chief feature of the Cordylophora from Lake Qurun is 

 the great vigour of the colonies, the hydrocaulus in some 

 attaining the height of 8 or 9 cm. ; branches of the tliird 

 order are common and as many as three or four gonophores 

 are frequently found below one lateral hydranth. The great 

 develoi)ment of the colonies is no doubt due to the salinity of 

 the water, which, altiiono-h not very high (r34 jjer cent.), 

 evidently suits tiie hydroid admirably, and the Cordylophora 

 certainly shows no tendency to invade the freshwater canals 

 which enter the lake ; I made a careful examination of reeds 

 and logs of wood at the mouth of the " Wadi," and never 

 found the hydroid in this situation. 



Cordylophora lacustris has not been recorded from the Nile ; 

 its occurrence in the Birket el Qurun is tiierefore of great 

 interest, the lake being nearly 150 miles inland, and at the 

 present day witiiout communication witli the sea except by 

 means of that river. 



Geological evidence, however, shows that in late Pliocene 

 times the depression in which Lake Qurun is situated must 

 have been of the nature of a large brackish fjord in communi- 

 cation with the Mediterranean ; it seems tiierefore possible 

 that Cordylophora first established itself in the district at 

 that period. This seems all the more probable when we 

 consider the present habitat of the species in broads and 

 estuaries. 



LXXTX. — ^l Sytwpsis of the SharJcs of the Family 

 Cestraciontidae. ]iy C. Tate Kegan, M.A. 



The Cestraciontidae may be diagnosed as sharks with two 

 dorsal fins, each preceded by a spine, an anal Hn, live gill- 

 openings on each side, the last two or three above the base 

 of the pectoral Hn, oro-nasal grooves, and the pterygo- 

 quadrate articulated to the prieorbital region of the cranium. 

 Two genera may be recognized. 



