THE LEPTOSTRACA 161 



"phyllopod" form of the thoracic limbs in the Leptostraca may 

 be to some extent secondary, having arisen by suppression of the 

 locomotor function in limbs of the more typical Malacostracan 

 form. In this case Paranebalia, in which the phyllopod character 

 of the thoracic appendages is very little marked, would be more 

 primitive than Nebalia and Nebaliopsis. 



It is difficult to decide how much importance should be given 

 to the presence of an adductor muscle as indicating an affinity 

 between the Leptostraca and the Conchostraca, but the possession 

 by the former of a mandibular palp and well-developed maxillae 

 forbid their being derived directly from any of the existing 

 Branchiopoda. 



As regards the relation of the Leptostraca to the various groups 

 of Eumalacostraca, there seems to be a general agreement that 

 their nearest allies are to be sought among the Mysidacea, which 

 they resemble especially in their mode of development. It may 

 be necessary to mention that, apart from a vague similarity in 

 general form, perhaps the result of a similarity in habits, there 

 is no ground for the supposition that they have any direct affinity 

 with the Cumacea. 



The four existing genera of Leptostraca may, for the present, 

 be referred to a single family. In the absence of information as 

 to the structure of the limbs in the fossil Ceratiocaridae, it is not 

 possible to assign them to a definite systematic position in relation 

 to the living forms. 



ORDER Nebaliacea, Caiman (1904). 



Family NEBALIIDAE. Nebalia, Leach ; Paranebalia, Glaus ; Nebaliopsis, 

 G. 0. Sars ; Nebaliella, Thiele. 



LITERATURE. 



1. Glaus, C. Ueber den Ban und die systematische Stellung von Nebalia. 



Zeitschr. wiss. Zool. xxii. pp. 323-330, pi. xxv., 1872. 



2. Ueber den Organismus der Nebaliden und die systematische Stellung 



der Leptostraken. Arb. zool. Inst. Wien, viii. pp. 1-148, pis. i.-xv., 

 1888. 



3. Metschnikoff, E. Development of Nebalia [Russian]. Zapiski Imp. Akad. 



Kauk. St. Petersburg (8vo series), xiii. 48 pp. 2 pis., 1868. 



4. Robinson, Margaret. On the Development of Nebalia. Quart. J. Micr. 



Sci. 1. pp. 383-433, pis. xvi.-xxi., 1906. 



5. Sars, G. 0. Report on the Phyllocarida. Rep. Voy. "Challenger," Zool. 



xix. 38 pp. 3 pis., 1887. 



6. Fauna Norvegiae. Vol. I. Phyllocarida and Phyllopoda, 4to, pp. 



vi + 140, 20 pis. Christiania, 1896. 



7. Thiele, Joh. Die Leptostraken. Wiss. Ergeb. deutschen Tiefsee-Expedi- 



tion "Valdivia," viii. 26 pp. 4 pis., 1904. 



8. Ueber die Leptostraken. Deutsche Siidpolar-Expedition, 1901-1903, 



Bd. ix. Zool. i. pp. 61-68, pi. ii., 1905. 



