ACICHELYID^. 1 51 



The above generic types are identified as belonging to one form 

 by Zittel in the ' Palgeontographica,' vol. xxiv. art. 5 (1877), who 

 also includes Paraclielys {infra, p. 195). The genus Aplax was 

 founded upon an embryo skeleton, and Achelonia upon a specimen 

 of the manus. The name Aplax is earlier than Acichelys, but is 

 inappropriate, as it was applied on the supposition that there were 

 no costal bones on the ribs. 



Acichelys redenbacheri, Meyer 1 . 



Syn. Eurysternum erassipes, Wagner ". 

 Palceomedusa testa, Meyer 3 . 

 ? Achelonia formosa, Meyer 4 . 

 P Euryaspis radians, Wagner 5 . 



The type species. In typical examples the neural bones of the 

 carapace show no distinct antero-lateral facets, and are long and 

 narrow. 



If this species be identical with Eury sternum wagleri, Meyer 6 , 

 that specific name should be adopted, but Eiitimeyer doubts if this 

 is the case. 



In an immature skeleton of this genus, figured by Zittel in the 

 1 Palaeontographica/ vol. xxiv. pi. xxvii., under the name of Eury- 

 sternum wagleri, Meyer, the neurals have distinct antero-lateral 

 facets. Zittel considers that specimen as specifically identical with 

 the present form ; but this difference may indicate a specific dis- 

 tinction. In that case there is no evidence to show whether that 

 specimen is specifically identical with Meyers E. wagleri. Neither in 

 the event of there being two species of the genus, is there any evidence 

 to show to which form Aplax oberndorferi, Meyer 7 , belongs. 



Hob. Europe (Bavaria). 



49155. Cast of a slab of limestone showing the imperfect skeleton 

 of an immature individual. The original was obtained 

 from the Lower Kimeridgian Lithographic stone of Kelheim, 

 Bavaria, and is figured in Meyer's ' Bept. Lith. Schiefer/ 

 pi. xx. fig. 1, as Palceomedusa testa., of which it is the type. 

 It is also the type of Eury sternum crassipes. As pointed out 

 by Eiitimeyer, there are no characters by which this spe- 

 cimen can be distinguished from the types of the present 

 species figured in pis. xix., xxi. of the same work. In 



1 Neues Jahrb. 1854. p. 579. 



2 Gelehrte Anzeiger, vol. xh'x. p. 553 (1859). 



3 Fauna tfer Vorwelt— Eept. Lith. Schiefer, p. 136 (1S60). 



4 Ibid, p. 140. 5 Abb. k.-bay. Ak. Wiss. vol. ix. pt. i. p. 89 (1861). 



6 In Minister's ' Beitrage z. Petrefactenkunde,' 1st ed. pt. i. p. 75 (1839). 



7 Neues Jahrb. 1843, p. 585. See also Eept, Lith. Schiefer, pi. xviii. fig. 2. 



