* Ortmann — Crangojpsis vermiformis. 285 



sally free, shows that closer relations exist to the Mysidacea 

 than to any other order. 



There is no doubt that the Carboniferous and Permian fossils 

 designated by Brocchi* as a new family (JVectotelsonidce) of 

 the order Amphipoda belong to that primitive group of Mala- 

 costraca which gave origin to the different now living orders. 

 This family contains the genera Palceocaris Meek and Worthen, 

 Uronectes Bronn (= Ganipsonyx Jordan), and Nectotelson 

 Brocchi, but its position among the Am phi pods, as maintained 

 by Brocchi, is certainly erroneous. The JVectotelsonidoe show 

 a number of characters common to all Malacostraca, but no 

 typical characters of any of the orders of this subclass ; they 

 represent a mere collective type of different Malacostracous 

 orders. 



The general characters of all Malacostraca are the following : 

 Body with a limited number of segments ; the number of the 

 anterior segment is somewhat doubtful, but there are certainly 

 eight segments of the " cormus " bearing the cormopods, and 

 seven of the abdomen or pleon, six of which bear pleopods, the 

 last one forming with thetelson a caudal fin. A differentiation 

 between the appendages of the cormus and the pleon is present. 

 This primitive type of Malacostraca is divided into two large 

 sections : the Thoracostraca, having a carapace developed and 

 stalked eyes, and the Arthrostraca having no carapace and ses- 

 sile eyes.f The first section is farther characterized by the 

 prevailing presence of the caudal fin (which is reduced only in 

 the Decapoda Brachyura); of the second section only a part of 

 the Isopods retains the caudal fin. In the Thoracostraca the 

 legs are either differentiated in the primitive manner into cor- 

 mopods and pleopods, or the former are again divided (Deca- 

 poda) into three maxillipeds and five pereiopods (thoracic legs). 

 In the Arthrostraca, there is never a differentiation of maxilli- 

 peds and pereiopods, but often (Amphipoda) the pleopods are 

 divided into swimming (anterior) and jumping (posterior) feet. 



The JVectotelsonidce of Brocchi show on the one hand the 

 primitive characters of the Malacostraca ; they have a limited 

 number of body-segments, divided according to the appendages 

 into a cormus and a pleon with a caudal fin. On the oilier 

 hand no carapace is developed and stalked eyes are present.;); 

 The latter character, and the shape of the antennae, and the 

 gill-like appendages on the bases of the cormopods separate 

 this group from the Arthrostraca, and Jordan and Meyer were 

 perfectly right in so far as giving Uronectes a position inter- 



*Bull.Soc. Geol. France, iii, 8, 1880. 



f I disregard the Cumacea, which are intermediate between both in this respect. 

 % The details of structure given here are best known iu Uronectes{= Gampsonyx). 

 Compare Jordan and Meyer, Pal aeon tographica, iv, 1, 1854, p. 1, ft. pi. 1. 



