356 Joseph Mawson — The Cretaceous of Bahia, Brazil. 



length, and is narrow and pointed, and its lateral lamella is rounder, 

 shorter, and broader, being 4 mm. in length. Tlie elongated 

 posterior part of the trunk, which is without limbs, and which in 

 Chirocephalus and Brmichinecta makes up half the length of the 

 animal, and consists of from seven to eight rounded segments destitute 

 of limbs, is not developed in the Eochdale specimen ; but in all the 

 Branchiopoda the number of trunk-somites varies greatly (from eleven 

 to nineteen in the Anostraca), whilst in the larval stages the number 

 of segments is often much fewer than in the adult, especially as 

 regards the apodal caudal segments. I think there is but little 

 doubt that this specimen represents a mature individual, but bearing 

 in mind the fact that it is of so great a geological age as the Coal- 

 measures, one would not be surprised to find that it may have 

 retained to some extent the larval characters of the family in its 

 adult condition ; the development of the caudal segments in later 

 geological times may probably be the outcome of a more active 

 lacustrine or pelagic life pursued by its descendants, and continued 

 down to the present day. 



The entire absence of a carapace, the form of the head, the probable 

 presence of pedunculated eyes, and the general arrangement of the 

 body with its branchigerous swimming-limbs, lead me to consider 

 that its appropriate zoological place is with the Branchiopoda, and 

 in the order Anostraca. 



It may be convenient to suggest a new genus for its reception, 

 and I would venture to propose the generic appellation of Rochdalia 

 as a record of the locality which has yielded so remarkable and so 

 rich a fauna ; and Parkeri for the specific name, after its discoverer, 

 who is one of the most enthusiastic of local collectors, and has added 

 so largely to our knowledge of the Carboniferous Invertebrata of 

 Lancashire. 



V. — Notes on thk Cretaceous Formation of Bahia, Brazil. 



By Joseph Mawson, F.G.S. 



(WITH A SKETCH-MAP.) 



riIHE Cretaceous formation of Bahia, first brought prominently to 

 X notice by the discoveries of Allport ' in 1859, has been in great 

 part examined and described by the late Professor Hartt,^ by Dr. 0. A. 

 Derby,^ by Dr. R. Rathbun,* and by Dr. J. C. Branner.^ Some 

 additional observations made by the present writer were published 

 in the Geological Society's Journal of May, 1907, to accompany 

 Dr. A. Smith Woodward's paper on the Vertebrate Fossils of the 

 formation. 



1 S. Allport, Quart. Journ. Geol. Soc, vol. xvi, p. 263, 1860. 



"^ C. F. Hartt, Geology and Physical Geography of Brazil, 1870. 



* 0. A. Derby, "A Bacia Cretacea da Bahia" : Archives do Museo Nacional, 

 Eio de Janeiro, vol. iii, p. 135, 1878. 



^ E. Bathbun, " Observagoes sobre a Geologia. Aspecto da Ilha de 

 Itaparica " : ibid., p. 159. 



^ J. C. Branner, " The Stone Beefs of Brazil " : Bull. Mus. Comp. Zool. 

 Harvard Coll., Geological Series, vol. vii, p. 150, May, 1904. 



