8 Prof. Allman on a new genus and species of Entomostraca. 



that it is composed exclusively of the epimerse, which in conse- 

 quence of the non-development of the tergum become confluent 

 in the mesial line of the back, presenting in one of the early 

 phases, as we have already seen, their original distinctness. 



The genus Notodelphys thus presents us with a most interest- 

 ing transitional form between the true Entomostraca and the 

 suctorial Crustacea. Its perfect mandibulate mouth will at once 

 place it with the former, a position indeed which its highly de- 

 veloped natatory feet and active habits as well as its general phy- 

 siognomy would in the first instance suggest. The form, on the 

 other hand, of the accessory oral organs or maxillary feet, which 

 are here constructed so as to constitute organs of attachment, as 

 well as the singular development of the dorsal arch of the poste- 

 rior thoracic ring, and the connection of the feet of opposite sides 

 through the intervention of a large intercoxal plate — a striking 

 feature in the greater number of the suctorial Crustacea and not 

 found in the Entomostraca — unite with the semiparasitical habits 

 of Notodelphys in indicating an affinity not to be mistaken with 

 the true suctorial tribes. 



In the whole of the description now given it has been thought 

 most convenient to adhere to the terminology in ordinary use, 

 though the researches of Erichson (Entomographien) have in 

 many particulars altogether disproved its correctness. The tho- 

 rax, for instance, according to the philosophic views of this na- 

 turalist, consist throughout the three classes of Insecta, Arach- 

 nida and Crustacea, invariably of three segments and no more, 

 but these often so consolidated with one another and with the 

 neighbouring segments, as to render it necessary to have recourse 

 to indirect indications in order to determine the real composition 

 of the part. Erichson has moreover shown that the true abdo- 

 men among the Crustacea includes several segments, hitherto 

 incorrectly supposed to belong to the thorax, and that it is for 

 the most part divisible into two very distinct regions, an anterior 

 and a posterior. To reduce the Entomostraca to the type of In- 

 secta is believed by Erichson to be one of the most difficult 

 problems in zoology. In attempting its solution he maintains 

 the consolidation of the head with the thorax, and adopts the 

 singular though apparently correct opinion, that the anterior 

 pair of thoracic legs is invariably placed before the mouth. 



In applying these original and philosophic views to the deter- 

 mination of the true import of the various parts in the Entomo- 

 stracan which forms the subject of the present paper, we will 

 have the first pair of thoracic legs represented by the prehensile 

 appendages which immediately succeed the antennae; behind 

 these is the mouth with its mandibles and first and second pair 

 of maxillse, and then come two pairs of prehensile appendages, 

 which are the second and third pairs of thoracic legs ; all the 



