224 THIi: AMERICAN MIDLAND NATURALIST 



Tigs. 23-25. — Douvillina arcuata maxima. Pedicle (ventral) and lateral 

 views of a large cotype. 25, posterior view of same posed to show 

 irregularity of shell margin. 

 Figs. 26-31. — Spirijer orestes Websteri. 



26. — Anterior view of a coarse and somewhat deformed specimen. 



27. — Anterior view of a wide and fine specimen. 



28-29. — Detail views of shell and sinus of another cotype. 



30. — Enlarged detail of sinus of specimen shown in fig. 27. 



31. — Enlarged detail of portion of shell of specimen shown in fig. 26, 

 showing bifurcation of plications. 



EXPLANATION OF PLATE VII. 



Figs. i-2a. — Small specimens of Naticopsis gigantea Hall and Whitfield. 

 Fig. 3. — Large and partially restored specimen of Naticopsis gigantea Hall 



and Whitfield. 

 Fig. 4. — Floydia concentrica multisinuata. Holotype. 



Fig. 5. — Floydia concentrica Webster. 5a, cross section of shell of body 

 volution of specimen shown in fig. 5. 

 (For further discussion of these figures see under Floydia concentrica 

 Webster.) 



All figures natural size unless stated otherwise. 



Charles City, Iowa. 



Heterothrix (B. L. Robins) Rydb. a Synonym, and Other Notes. 



BY J. A. NlEUWLAND. 



The name Heterothrix Muell., Arg. in Mart. Fl. Bras. VI., 133, 

 t. 40 (i860), antedates the same name used by Rydberg 1 in his 

 "Flora of the Rocky Mountains" for the section Heterothrix of 

 Robinson raised to generic standing. To replace the invalidated 

 name may be suggested that of Pennellia in honor of Francis W. 

 Pennell. 

 Pennellia Nwd. 



Heterothrix (B. L,. Robbins) (19 17) Rydb. not Heterothrix 

 Muell. 1. c, (i860). 



Pennellia micrantha (A. Gray) Nwd. 



Heterothrix micrantha (A Gray) Rydb., 1. c. 

 Thelypodium micranthum (A. Gray). 

 In some instances considerable freedom has been used in changing 



1 Rydberg, P. A., "Flora of the Rocky Mountains and Adjacent Plains." 

 New York, 19 17. 



