DESCRIPTIONS OF SPECIES. 417 



AVICULOPECTEN Sp. CI. 



PI. VIII, fig. 2. - 



Of this little shell we have only the specimen which is illustrated by fig. 2 of PI. 

 Vni. I have not been able to refer it satisfactorilj^ to any of our numerous pectinoi'd 

 species, but it seems to be closely related to A. coxanus Meek and Worthen. I would 

 scarcely consider it identical with the Nebraska form which Meek identified with A. 

 coxanus, but it so closely resembles the figure of the original reference that I would 

 probablj' have referred it to Meek and Worthen's species if it were not that in their 

 figure the ears are clearly shown to be marked with radiating ribs, a character which 

 my specimen does not possess. Besides this character, it differ's from the Nebraska 

 form in having the striee finer and more crowded. Of these, there are 17 or 18 in the 

 space of 5 mm. Thej' are thin and sharp, somewhat alternating, and separated by 

 intervals slightly greater than their own thickness. There are also faint concentric 

 growth lines, and these are the only markings which appear upon the rather broad 

 ears. 



Locality and horizon. — Ouray (station 2194); Hermosa formation. 



AVICULOPECTEN Sp. 0. 



From Ouray we have a single specimen of an undetermined but fine and striking- 

 species of Aviculopecten. The fossil is crushed and very imperfect, and its configu- 

 ration can not be ascertained. It is a large shell, however, and must have had a 

 length of -45 mm. or more. The surface is marked by coarse, regular, somewhat 

 flattened, rigid ribs, of which near the outer margia there are about 6 or 7 in the 

 space of 10 mm. They are separated by flat shallow grooves about as wide as, or 

 sometimes a little wider than, the intervening ribs. The whole is crossed at intervals 

 of about 1 mm. by verj^ regular, strongly lamellose concentric strite. 



This is a fine, large, and well-characterized species, and, as far as I have ascer- 

 tained, it is as yet undescribed. 



Locality and layrlzon. — Ouray (station 2194); Hermosa formation. 



ACANTHOPECTEN new subgen. 



This name is proposed to receive Aviculopecten carhoniferus Stevens, and while 

 at present no higher significance is assigned to it than as subgeneric to Aviculopecten 

 (or possibly Lima) it is not improbable that it will subsequently be found to take 

 rank as an independent genus. 



The large, angular plications of this species and its spinose rim and growth lines 



give it an fepression so strongly marked that even upon the consideration of its 



superficial characters I would be disposed to separate it from the more usual types 



referred to Aviculopecten, and Meek, who was, I believe, the first to suggest that it 



14364— No. 16—03 27 



