XV TENTACULATA CYDIPPIDEA 4 I 7 



a height of 250 mm., and Cestus veneris has been found no less 

 than 1^ metres from one extremity to the other. 



Ctenophores usually go about in shoals, and in the case of 

 Beroe cucumis and Eucharis multicornis the shoals may be of 

 very great extent. Pleurobrachia pileus of the British coasts 

 is often found at the end of the season (July) as a series of 

 isolated individuals ; but in June they occur in small shoals, 

 swimming so close together that they will choke a tow-net in a 

 very short space of time. 



CLASS I. TENTACULATA 



Ctenophora provided with a pair of tentacles in the larval 

 stages only or in both larval and adult stages. 



Order I. Oydippidea. 



This order includes a number of spherical or oval Ctenophores, 

 with a pair of tentacles retractile into deep tentacular pits in the 

 adult stage. 



Fam. 1. Mertensiidae. — The body is compressed in the trans- 

 verse plane, and the ribs on the transverse areas are longer than 

 those on the sagittal areas. The family includes the genus 

 Euchlora, which occurs in the Mediterranean and in the northern 

 part of the Atlantic Ocean. In Charistephane there are only two 

 enormous ctenophoral plates in each of the longitudinal tracts. 

 These plates are so broad that they almost meet laterally to 

 form two continuous circlets round the body of the animal. This 

 genus is found in the Mediterranean, but a few specimens have 

 also been obtained in the Atlantic. 



In Tinerfe the body is almost cylindrical, and there is a pair 

 of kidney-shaped swellings at the sides of the aboral pole. It 

 has a pale blue colour, and is found in the Guinea and south 

 equatorial currents of the Atlantic Ocean. 



The name Mertensia has been given to several forms that are 

 undoubtedly the young stages of genera belonging to the Lobata, 

 but Chun retains the name M. ovum for a species which is very 

 abundant in the Arctic currents of the North Atlantic. 



Fam. 2. Callianiridae. — Two or four wing-like processes, into 



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