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PROCEEDINGS OF THE NATIONAL MUSEUM 



group, Lepidocaris (Scourfield 1926), Opahinia differs in numerous 

 characters as mentioned below. 



2, General form and size. 



The general appearance of Opabi7iia as shown particularly in the 

 laterally compressed specimens and indicated in the conjectural 

 restoration (fig. Za) must have been very close to that of modern 

 Anostraca. In size it was larger than the majority of modern 

 species, but female specimens of Branchinecta ferox (Milne 

 Edwards) may reach 70 mm. in length (Daday 1910), which size is 

 almost identical with that of the best preserved female Opahinia 

 regalis. The large size of all the Anostraca is in striking contrast 

 to that of the minute Lipostracan LepidocaHs. 



FiorRE 3. — Palaeanostraca. a, Opabinia regalis Walcott, conjectural restora- 

 tion. (About X 1%.) 6, Rochdalia parkeri H. Woodward X 4 (after Wood- 

 ward, BY Courtesy of the Editor of the Geological Magazine.) 



3. The presence of pedunculate eyes. 



This is the most diagnostic character of the Anostraca among the 

 orders of Branchiopoda and is amply fulfilled by Opahinia. No eyes 

 are known in Lepidocaris, while the other orders all have sessile eyes. 



4. The position of the antenna and the probable reduction of the 

 antennule. 



If these structures have been rightly interpreted Opabinia more 

 closely resumbles the Anostraca than any other group. 



5. The nearly uniform series of foliaceous trunk limbs . 



This condition is characteristic of most of the " phyllopod " 

 Branchiopoda. 



6. The presence of a frontal process which was probably confined 

 to the male. 



