242 PROCEEDINGS OF THE ACADEMY OF [1888. 



CEPHALOPODA. 



Orthoceras rushensis McChesney. 



Orthoceras rushensis McChesney, 1860. New Palse. Fossils, p. 68. 



Orthoceras rushensis AVliite, 1884. Geol. Report Ind. for 1883, p. 

 164. 



Specimens of this, and perhaps other species, often occur quite 

 abundantly. The specific characters of the described species of 

 this genus are so obscure that all attempts to separate many of the 

 so-called species prove futile. A careful comparison of the carbon- 

 iferous forms Avill doubtless lead to a considerable increase in the 

 synonymy of this group, and a reduction of the number of species to 

 four or five. 



Orthoceras (sp. und.) 



A single specimen from the Pioneer mine ; it is nearly 50 cm. in 

 length and has a diameter at the larger extremity of about 5 cm. 

 It is by far the largest specimen of this genus yet observed in the 

 carboniferous rocks of Iowa. 



Nautilus lasallensis Meek and Worthen. 



Nautilm lasallensis Meek and Worthen, 1866. Proc. Acad. Nat. 



Sci. Phila., p. 261. 

 Nautilus lasallensis Meek and Worthen, 1873. Geol. 111., vol. V, 



p. 610. 

 Quite common at the Giant mine ; but few of the specimens are 

 in a very good state of preservation. 



Nautilus oocidentalis Swallow. 



Nautilus occidentalis Swallow, 1858. Trans. St. Louis Acad. Sci., 



vol. I, p. 196. 

 Nautilus quadrangularis McChesney, 1860. Disc. New. Palse. 



Foss., p. 65, 

 Nautilus nodocarinatus McChesney, 1860. Disc. New False. Fos., 



p. 66. 

 Nautilus hiserialis Hall, 1860. Geol. Iowa, Supp., p. 92. 

 Nautilus occidentalis McChesney, 1867. Trans. Chicago Acad. 



Sci., p. 57. 

 Only a single specimen has thus far been found at Des Moines. 



Nautilus winslovi Meek and "Wortlien. 



Nautilus (Teimiocheilus) winslovi Meek and Worthen, 1870. Proc. 

 Acad. Nat. Sci. Phila., p. 50. 



