342 ME. W. T. CALMAK ON THE CHAEACTEES 



the position of the genital apertures, the characters of the 

 thoracic limbs, and the presence of appendages on the terminal 

 somite of the abdomen, appear to afford conclusive evidence on 

 this point. The possibility that it may be a larval form, as 

 Moniez * has suggested, is excluded if the identification of the 

 genital apparatus be correct ; but it may be remarked that, as a 

 larva, Bathynella would be no less unique than as an adult 

 crustacean. 



Assuming for the present that we have to deal with an adult 

 form, it is clear that it cannot be received into any of the 

 divisions of the Malacostraca as commonly defined. The appa- 

 rent similarity to the Arthrostraca in the segmentation of the 

 body, which led its discoverer to compare it to an amphipod, 

 disappears when it is recognized that the first thoracic somite is 

 free from the head and that the appendages carried by it are not 

 specialized as maxilhpeds but resemble the succeeding thoracic 

 limbs. 



The presence of natatory exopods and of external epipods on 

 most of the thoracic limbs are further characters not shared by 

 any of the Arthrostraca. The other divisions of the Malaco- 

 straca agree in possessing a carapace with which one or more 

 of the thoracic somites are usually united dorsally. While some 

 of them show isolated characters in common with Bathynella, 

 as, for example, the free first thoracic somite of Nebalia and 

 some Stomatopods, the natatory thoracic exopods of Schizopoda, 

 Cumacea, and some Decapods, the undifferentiated n)axillipeds of 

 Euphausiidse, and the plate-like epipods of Stomatopods, these 

 resemblances are accompanied by differences so profound that 

 there can hardly be any question of immediate affinity. 



While our ignorance of many points in the structure of 

 'Bathynella^ more especially as regards the mouth-parts, pre- 

 cludes for the present any definite conclusion as to its precise 

 systematic position, the characters already ascertained suffi- 

 ciently show that we have to do with a very peculiar and isolated 

 type without close affinities to any of the recognized divisions of 

 the Malacostraca. It appears to me, however, that some light 

 may be thrown on its relationships by a comparison with the 

 anomalous " schizopod " Anaspides tasmania of Mr. G. M, 



* Eev. Biol, du Nord de la France, i. 1888-89, p. 253. 



