COLLECTED BY CAPTAIN TOYNBEE. 176 



seem to show that it is in reality more nearly allied to the typical Calani. More- 

 over, in certain Calani (as, for instance, in C. elongatus) the anterior antenna bears 

 here and there long setse, almost as in EuchcBta. G. latus seems therefore, to me, to 

 form an interesting link between the two above-named genera. The Calanidse, many 

 as are the species which yet remain to be discovered, present us with a very perfect 

 gradation of forms; and indeed the whole tribe of Cyclopoidea offers in this respect 

 a marked contrast to the Cyproidea. This latter group is at present poor both in 

 genera and in existing species, and it is in many respects very aberrant. The Cyclo- 

 poidea, on the contrary, contain an immense number of species, which, as I have just 

 remarked, form a somewhat complete series, or rather network. In this great family, 

 then, it would seem that most of the types are still existing, that there has as yet been 

 no very great amount of extinction, and that the type is not, geologically speaking, very 

 ancient. The nature of the body is certainly not favourable for preservation, and nega- 

 tive evidence is of very little value in geology ; still it is worthy of remark that the 

 group, now so numerous, has not as yet any known extinct representatives, though, from 

 the great diflFerences between some of the existing species, we may safely infer that the 

 group is of considerable antiquity. The Cyproidea, on the contrary, are known to have 

 existed as early as the Silurian period. They are therefore a very ancient type ; a great 

 proportion of the known species are fossil; and as the soft parts are never preserved, 

 we cannot expect to recognize among them more than a few of the links which must 

 have connected the diflFerent genera with one another, and the whole group with what we 

 now consider the more normal Crustacea. 



Diaptomus ? abdominalis, again, is obviously a link between Diaptomus and the species 

 placed by Dana in his genus Hemicalanus and the ordinary Calani, — possessing, as it does, 

 the second maxillae and second antennse of the latter, with the geniculating anterior 

 antennae and abnormal posterior legs, which are characteristic of the former. Indeed, 

 unless it is admitted to constitute such a Imk, it must be considered as the type of a 

 new genus. I did not, however, adopt this view in 1856, nor am I disposed to do so 

 now. Such a coiu-se, if followed in other similar cases, would lead to an immense and 

 at present unnecessary multiplication of genera. This species, moreover, even " if called 

 by any other name," would be just as much intermediate between the above-named genera 

 as before. In order, however, to retain this species in the genus Diaptonms, it will be 

 necessary to modify the generic character given by Dana, in so far as concerns the pos- 

 terior legs of the females. 



The structure of the anterior antennae, again, is intermediate between that of Calamts 

 and that of Pontella. The right antenna differs slightly from the left, and may perhaps 

 be rightly described as geniculating ; but the prehensile power must be very small. 



The second pair of antennae have the two branches equal. The mandibles and first 

 pair of maxillae resemble those of Calanus brevicornis (Trans. Ent. Soc. n. s. vol. iv. pi. 3. 

 f . 3 & 4). The second pair of maxilla? and maxillipeds are as in Calamis; the latter 

 has the terminal segments elongated. Mrs. Toynbee's collection included no mature 

 males. The fifth pair of legs in the females [1. c. pi. 10. f. 6.) difl'er slightly from those 

 originally figured by me. The present specimens, however, were rather smaller, and 



2 a2 



