162 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.xxii. 



and was at first regarded by the writer as a variety of that form. M. 

 arcticus is, however, nearer subquadrate than ovate, shorter and more 

 erect, the post-cardinal portion more alate, and the beaks smaller and 

 more pointed than in M. patulus Ulrich. 



Collector.— J. K Carpender. Cat. No. 28166, U.S.i^.M. 



WHITEAVESIA SYMMETRICUS, new species (Ulrich). 

 (Plate XIII, tigs. 15-17.) 



This little shell was thought by the writer to be probably identical 

 with Crytodonta affinis var. Jillmorensis Ulrich,^ and for confirmation of 

 this opinion sent the specimen to Mr. Ulrich. He, however, refers it to 

 the genus Whiteavesia of the family Modiolopsidse. As his notes are 

 detailed, they are given at length. 



Remaius of the hlack ornament-hearing epidermis prove the specimen to helong 

 to the Modiolopsidse. It is a new species, with an anterior end reminding of Modio- 

 lopsis argnta, while the rest of the outline and general aspect is more nearly like M. 

 similis. It is also like M. obsoleta, but it is too high posteriorly. It is, however, 

 not a true ModioJopsis, the umbones being too prominent and full, the ventral outline 

 convex, and the anterior muscular scars scarcely distinguishable in the cast. These ' 

 characters make it a Whiteavesia, and it does not seem to be closely related to any of 

 the described species of that genus. The rather uniform convexity of the valves is 

 peculiar to this species. 



Collector.— J. N. Carpender. Cat. No. 28162, U.S.N.M. 

 Family CYRTODONTID^ Ulrich. 



CYRTODONTA SILLIMANENSIS, new species (Ulrich). 

 (Plate XIII, figs. 31-33.) 



Mr. Ulrich has kindly made the following notes on this species: 



Have compared this with every Cyrtodouta known to me without finding one 

 with which it is identical. In a general way it reminds of C. afflnis, C. parva, and 

 C. halli;- but am satisfied it is not closely related with any of that group of species. 

 Its true affinities seem to be with C. snbcariiiata Billings, but is readily distinguished 

 by its shorter form and much broader posterior. From C. liuronensis Billings,^ which 

 I regard as another close ally (also C Mllingsi Ulrich -), it differs not only m size but 

 in its greater convexity and much better defined antero-median sulcus. The speci- 

 men is preserved in part as a cast of the interior, and I am therefore inclined to 

 doubt that the sulcus is as strongly defined on the exterior of the shell as shown on 

 the specimen. 



Collector.— i. N. Carpender. Cat. No. 28159, U.S.N.M. 



CYRTODONTA (?) GIBBERA Ulrich, variety. 



(Plate XIII, figs. 34-36.) 



Cyrtodonta gibhera Ulrich, Geol. Minn., Ill, Pt. 2, 1894, p. 542, pi. xxxix, 

 figs. 13-15. 



The only example of this species was sent by the writer to Mr. Ulrich, 

 who made the following comparisons : 



' Geol. Minn., Ill, Pt. 2, 1894, p. 540, pi. xxxix, tig. 23. 



-Ibidem. 



'Canadian Nat. and Geol., Ill, 1858, p. 432. 



