ART. 27 NEW MIDDLE CAMBEIAN FOSSILS — EXJEDEMANN 7 



Other important characters of Mania are the immense develop- 

 ment of two swimming arms (first and second pair of antennae, see 

 fostea) ^\\\Q large imsegmented head with carapace (possibly cephalo- 

 thorax) bearing a single eye, five pairs (or less) of legs, a simple 

 abdomen, consisting of about seven segments, and the absence of a 

 telson. 



It is customary to refer the earlier Paleozoic crustaceans to the 

 suborder Phyllopoda of the order Branchiopoda, because these are 

 the oldest and most primitive crustaceans. [The recent genus Apus, 

 or Lepidurus^ has been traced to the Permian (Ruedemann, 1922).] 

 There is indeed a close resemblance to the family Limnadiidae of the 

 Phyllopoda — particularly to Limnetis in the biramous, strongly 

 developed second antennae, the single (not bivalved) carapace, the 

 fused compound eyes in the middle of the head, and the small num- 

 ber of thoracic feet. Although a telson is present in Limnetis, in 

 L. hrachyura it is so small that this species appears but little differ- 

 ent from our specimens in this respect. The body of the Limnadi- 

 idae is, however, laterally compressed and the carapace covers most 

 of it. 



According to common consensus of opinion the Limnadiidae lean 

 toward the second suborder of the Branchiopoda, the Cladocera. 

 Marria also has important characters in common with Cladocera, 

 namely, the strong development of the biramous second antennae 

 into principal organs of locomotion, the fused compound eyes, and 

 the short body with a small number of thoracic limbs. Though the 

 Cladocera have a telson, it is variable in size and in some species 

 much reduced. The carapace is likewise variable, for while it is 

 most frequently a bivalve shell inclosing" the whole postcephalic 

 region of the bodj^ it may be reduced to a mere brood pouch, as in 

 Leptodora. The segmentation of the body is little pronounced, if 

 not obscure, the thorax bearing as many pairs of limbs as there are 

 segments ; the abdomen having but three segments, bearing no limbs, 

 but with a telson. The head in the Cladocera, however, is always 

 bent downward so that the first pair of antennae and the median eye 

 are on the ventral side. 



It will be seen that our form, though not directly referable to the 

 Cladocera, agrees well with that order in the development of the 

 second antennae, the carapace (aside from its common bivalve form 

 in the Cladocera), the fused eyes, the small number of segments, and 

 thoracic limbs. It would seem to differ in not possessing the down- 

 ward bend of the head or a telson. 



Our species also invites comparison with the second order of 

 crustaceans, the Copepoda, in regard to the possible retention of the 

 single nauplius ej'e, the strongly developed biramous second pair of 

 antennae, and the possible absence of a carapace. The Copepoda 



