200 The AMERICAN MIDLAND NATURALIST 



Fig. 27. Spirifer websteri Fentoii. Rockford, Iowa. A distinct species of 

 the orestes group. I originally referred to this form the one shown in 



Figs. 28-31, but this was incorrect. 

 Figs. 26; 28-31. Spirifer species undescribed. Rockford, Iowa. Another 



species of the group of S. orestes H. & W. Spirifer zone; about equally 



characteristic of Rockford and Hackberry Grove. 



Explanation of Plate 



Fig. I — 2a. Naiicopsis giganlea Hall and Whitfield. Hackberry Grove, la. 



Fig. 3. Naiicopsis giganlea Hall and Whitfield. A large specimen, upper 

 whorls restored. Hackberry' Grove, Iowa. 



Fig. 4. Floydia concentrica mullisinuaia'Feriton. Holotype. Rockford, Iowa. 



Fig. 5. — 5a. Floydia coticenlrica Webster. Fig. 5; portion of a large speci- 

 men. Fig. 5a; cross-section of shell of specimen shown In Fig. 5. Rock- 

 ford, Iowa. 

 Figures 1-3 are characteristic Spirifer zone forms from Hackberry Grove. 



Figures 4-5 show two typical specimens from the upper part of the Spirifer 



zone at Rockford. 



A Consideration of Certain Genera Proposed by Ehrhart. 



BY HOMER D. HOUSE 



The question of vi^hat constitutes proper publication of a genus 

 has received more than a little attention both in codes, proposed, 

 promulgated or adopted, and by individual expression of opinion. 

 A new genus published today without description but merely b)^ 

 the implication or indication of a type species would certainly 

 seem inadequately published. However any code or set or rules 

 which is retroactive is sure to encounter perplexing situations, 

 which lead sooner or later to various evasions or deliberate 

 exceptions. 



This article deals with a set of generic names published by 

 Friedrich Ehrhart in 1789 (Beitrage zur Naturkunde und den 

 damit verwandten Wissenschaften, etc. 4: 146-148. 1789). Like 

 many genera published by Rafinesque, Swe2t, and several other 

 early writers these genera were published without description, 

 merely by the designation of a previously published species. The 

 frequency with which this sort of generic publication occurs in- 

 dicates that it must have been at the time regarded as a quite 

 proper method. Many of Necker's genera are now regarded as 



