J. D. Tothill—The Ancestry of Insects. 387 



Schuchert, diaries 



1915. Pirsson-Schuchert, Text-Book of Geology : Historical geology, 

 New York (Wiley and Sons). 

 Viallanes, H. 



1890. Sur quelques points de l'histoire du deVeloppement embryon- 

 naire de la Mante religieuse (Mantis religiosa), Rev. Biol. Nord. 

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 Walcott, Charles D. 



1911. Middle Cambrian Annelids, Smiths. Misc. Col., vol. lvii, No. 5. 



1912. Middle Cambrian Branchiopoda, Malacostraca, Trilobita, and 

 Merestomata, ibid., No. 6. 

 Wheeler, William Morton. 



1889. The embryology of Blatta germanica and Doryphora decem- 

 lineata, Journal of Morphology, iii, September, No. 2. 



1892. On the appendages of the first abdominal segment of embryo 

 insects, Trans. Wisconsin Acad. Sci., Arts and Letters, vol. viii, 

 pp. 87-140, 3 pis. 



Art. XXXIX. — Some Characters of the Apical End of 

 P seudorthoceras hnoxense McChesney / by George H. 

 Girty.* With Plate I. 



Specimens showing the apical end of uncoiled cephalopods 

 are as a rule very rare. It is then somewhat in the nature of 

 an exception that the apical end of P seudorthoceras Tcnoxense 

 is not uncommonly preserved. The specimens that I have 

 heretofore examined, however, show very little save that instead 

 of tapering regularly, or if not regularly at least symmetrically, 

 to a point, they are obliquely truncated so that the apex is not 

 central but lies almost in the periphery. 



There have recently come into my hands two specimens 

 which show characters that have not previously been observed. 

 Though the characters are not new to the group as a whole, 

 but on the contrary are in accord with those of the few types 

 on which Hyatt and others have made observations, they 

 nevertheless seem deserving of record. These specimens were 

 found weathered out of shale and they have had the original 

 shell replaced by pyrite, a form of preservation particularly 

 favorable to the retention of the finer surface structures of 

 fossils. They were collected from the Des Moines group of 

 the Pennsylvanian series near Des Moines, Iowa, and were sent 

 to me by Mr. G A. Larson, of whose generosity I avail myself 

 of this occasion to make recognition. 



The better of the two specimens shows the usual oblique 

 truncation, the end being compressed so that a section across it 



* Published by permission of the Director of the U. S. Geological Survey. 



