SYSTEMATIC ARRANGEMENT. 29 



their form and structure, of a remarkable kind, as 

 indicated in the life-history of Lerndsa already referred 

 to. In the family Lernseidse the body of the adult 

 female is greatly distorted, and the head is buried 

 deeply in the tissues of the host; on the other hand, 

 the mature male, which, as shown in Plate XLII, 

 fig. 5, closely resembles the young female before it has 

 begun to assume that abnormal development charac- 

 teristic of the adult stage, does not, so far as known, 

 undergo any further change, but continues during its 

 short life to retain its normal structure and form. 

 The Chondracanthidas differ from the other two 

 families by the manner of their fixation, arid also by 

 the peculiar form of the mandibles, which are unlike 

 those of any of the other parasitic groups described 

 here. The Lernseopodidse are also distinguished by 

 their mode of fixation, as shown elsewhere. 



The Linnsean species Lern&a asellina, which was 

 ascribed by Blainville and Baird to Lernentoma, and 

 by Nordmann and others to Chondr acanthus, was re- 

 moved to a new genus, Oralien, by Bassett-Smith, on 

 account of some peculiar structural differences. But 

 while appreciating this, and after carefully comparing 

 the characters of Or alien with those of the older genus 

 Medesicaste Kroyer, we are inclined to think that the 

 difference between them is scarcely of sufficient im- 

 portance for the establishment of a new genus a 

 conclusion previously come to by Brian.* We have 

 therefore transferred this Linnaean species to Kroyer 's 

 genus Medesicaste. Moreover, as Splnjrion appears to 

 be a true Lernsean rather than a Chondracanthian 

 genus, with which family it is sometimes associated, 

 it has been transferred by us to the family Lernseidse. 



* ' Copepodi parassiti del Pesci d'ltalia/ p. 94. 



