370 ME. E. S. COBBOLD ON THE [vol. lxxvi, 



The Fauna of the Olexellus Limestone op Comley. 1 



Micromitra (Paterina) labradorica. I Bradoria (?) sp. indet. 



Micromitra (Paterina) minor. Microdiscus amnio. 



MicromitrafPatemnaJminorv&r.gibba. > Microdiscus attleborensis. 



Obolus par vulns. ' Micmacca (?) ellipsocephaloides. 



Obolella atlantica var. comleyensis. \ Micmacca (?) ellipsocephaloides var. 



Hyolithus (Orthotheca) compressus. senior. 



Hyolithellus micans. j Micmacca (?) ellipsocephaloides Tar. 



Helenia cancellata. spinosa. 



Scenella elevata. i Micmacca (?) ellipsocephaloides var. 



Helcionella rugosa var. comleyensis. strenuelloides. 



Latoiichella costata. \ Micmacca (?) parvula. 



Leperditia (?) dermatoides (?). i Callavia callavei. 



Leperditia (?) lenticularis. ] Callavia cf. callavei. 



Escasona (?) spp. indet. ! Callavia caHlandi. 



There are obvious connexions between this fauna and that 

 immediately below. Micromitra labradorica, Obolella atlantica 

 var. comleyensis, Helcionella rugosa var. comleyensis, Micro- 

 discus attleborensis, and Callavia callavei have already appeared 

 in ACj, from which, however, the five forms of Micmacca, as "well 

 as the less frequent other fossils, are all absent, and one or more 

 species of the Mesonacidse, not appearing in the Olenellus Lime- 

 stone, are present. 



On comparing the Ac., fauna with those above it, there is a 

 similar connexion observable, and to a considerable extent through 

 the same species, but Micmacca is absent in the superior horizons, as 

 also is Microdiscus attleborensis, their places being taken in horizon 

 Ac, by Strenuella • pustulata and Microdiscus belli marginatus. 



The faunas of the two next higher horizons, Ac 4 and Ac 5 , are 

 ■connected Avith the datum-fauna Ac, by Micromitra labradorica, 

 Obolus parvulus, Helenia cancellata, Latoucliella costata, and 

 also by numerous fragments referred with reserve to Callavia 

 callavei. Notwithstanding this connexion, the faunas of the 

 Strenuella and the Protolenus Limestones (Ac, & Ac., see p. 371) 

 are very distinct from those below and also one from the other. 

 In Ac, occur three species of Strenuella, Microdiscus lobatus, 

 M. speciosus, Lingulella viridis, Obolella atlantica var. trans- 

 versa, Hyolithus (Orthotheca) bayonet var. striata, and Salopiella 

 obliqua, none of which have been seen before ; and in Ac 3 occur 

 two species of JProtolenus, two of Mohicana, Microdiscus comley- 

 ensis, Hyolithus crassus, H. sculptilis, H. (O.) bayonet, Salterella 

 (?) bella, S. (?) striata, Latouchella striata, and Helcionella 

 cingulata, all of which are confined to the horizon. Strenuella 

 has entirely disappeared, as also has Obolella atlantica. 



Note. — In the foregoing paragraphs all mention of Hyolithellus micans 

 has been omitted, in order to avoid repetition. Forms referred to this species 



1 In Cobbold, 1911 b, p. 298, this fauna was tabulated under the title 

 '■ Helena Group.' A specimen has now been found of the pygidium then 

 assigned to Microdiscus helena "Walcott, attached, with three thoracic seg- 

 ments, to a cephalon then referred to Ptychoparia. (?) attleborensis Shaler & 

 Fcerste. The name Helena is, therefore, now abandoned. 



