separation of Perciformes for which it is a characteristic. Hence one can 

 suppose that Capsalidae separated approximately not before the Paleocene. 

 Dionchidae separated from Capsalidae or from ancestors close to them 

 (see page 272). Judging from their occurrence this took place not before 

 the Eocene and perhaps even somewhat later. The last family of the present 

 suborder--Loimoidae (see page 370), if indeed it actually belongs to it, 

 has a number of such singular traits that it is not possible to doubt its very 

 early separation from the common trunk even if it were earlier than the 

 separation of Monocotylidae, if they are judged by their contemporary 

 distribution on the hosts. 



Thus, the second suborder of Dactylogyridea has apparently a 

 somewhat older origin than the first in spite of the great specialization of 

 the families which comprise it. 



Thus, we have analyzed correlations within the limits of the 

 first subclass, attempting to determine not only the limits of the separate 

 groups which compose it but also the time of their formation. We now pass 

 to Oligonchoinea. Of three orders composing this subclass we have already 

 judged in detail the time of the separation of Chimaericolidea in the beginning 

 of the present chapter. As was already mientioned, Dlclybothriidea have 

 common ancestors with Chimaericolidea. Their separation probably was 

 very ancient. Taking into consideration that their basic progressive family, 

 Hexabothriidae, is initially linked with Elasmobranchii and widely distributed 

 on them, and also that it has a number of secondarily simplified peculiarities 

 of organization one can think that the appearance of ancestors of Hexabothriidae 

 took place somewhat before the separation of the contemporary Selachii from 

 their extinct ancestors. Hence, taking into consideration that the contempo- 

 rary Elasmobranchii are known from the lower Jurassic one can conclude 

 that Hexabothriidae became separated at any rate not later than the Triassic. 

 The second family of this order--Diclybothriidae is younger and undoubtedly 

 descends from ancestors very close to the first. Taking into consideration 

 the data about occurrence, one can suppose that its appearance approximately 

 in the Cretaceous period is very probable. 



Finally, the last, the order Mazocraeidea, very numerous in 

 contrast to the two examined before, descends from Chimaericola-like 

 ancestors beyond any doubt, and naturally falls into two suborders, 

 apparently formed independently and thus possibly deserving elevation to a 

 higher rank. Let us note, however, that this is not done by us for a number 

 of reasons, (see page 417) and especially because of the insufficient study 

 of the embryonic development of both suborders. As regards Mazocraeinea p. 458 

 this suborder is more ancient than the Discocotylinea. As confirmation 

 for this serves the nature of the primary distribution of Mazocraeidea 

 (dae? nobis) as well as the structure of the attaching apparatus, especially 

 of its chitinous parts (see pages 417 and 423 ). It is most probable that the 

 separation of Mazocraeidae is connected with the separation of Clupeidae, 



549 



