■iM) CARBONIFERyUS FORMATIONS AND FAUNAS OF COLORADO. 



ASTARTELLA Hall, 1858. 



ASTARTKI,I>A ? (JUULKYI Whito. 



1878. AKliirldlaijitrli'iji. Wliitr, Acad. Nat. Sci. Pliiliiilelpliia, I'mc, ]i. 35. 



Coal Measures: Danville, 111. 

 1SSI1. Axhirlelhi gurleyi. White, V. S. Geol. (ieog. f^urv. Terr., Twelfth Ann. Kept., f(ir 1878, jit. 1, 

 ji. 160, ])1. 42, figs. 6a-h. 



Coal Measures: Danville, 111. . , 



A sing-le specimen t'l-oni the Rico formation, found at .station 2343, seems to 

 belong- to Astartdhi ? gurleyi, which it certainly closely resembles in configuration. 

 1 think it highljr probable that if the hinge characters of this species were known, it 

 would be found to belong to the genus Microdon. 



Local it ij iind horizon. — San Juan region (station 2343); Rico formation. 



SCAPHOPODA. 



DENTALIID^E. 



Owing, doubtless, to their comparative raritj^ and unimportance, the Paleozoic 

 Scaphopods have been recipient of less investigation than anj^ other group of the 

 Mollusca. 



Although, upon the system of sculpture and upon the conformation of the 

 tube, recent Dentalia have been divided into a number of subordinate or subgeneric 

 groups, these divisions have not, it is believed, been apj)lied to the fossil forms 

 occurring in our American Paleozoics. Many of the characters employed in 

 distinguishing the recent forms would be difficult to ascertain in the imperfect 

 preservation usuall}^ seen in fossils, and one whole class of them, the posterior 

 notches and slits not infrequently characterizing the more recent Dentaliidee, have 

 not been recorded as occurring in their Paleozoic representatives. The S3^stem of 

 surface ornamentation, therefore, seems to afford the most -available basis for 

 subdivision, and among the Cai'boniferous forms two, and perhaps three, different 

 tj^pes of surface ornamentation can be recognized; a, surface crossed by longi- 

 tudinal ribs or stria?; 5, surface crossed bj^ transverse, usually oblique, annulations 

 or strife; c, surface smooth or with growth lines only. 



For forms characterized by surface of the first type it seems clear that the 

 name Dentalium, sensu stricto, should be employed. For shells having surface 

 ornamentation of the second t3'pe the name Plagioglypta has recently been proposed. 

 1 am in doubt as to the propriety of referring shells of the third type to Plagioglypta; 

 still more doubtful of the propriety of withdrawing them under a new name or of 

 referring them to one of the genera or groups already established, as, for instance, to 

 Lsevidentaliiuii. The distinction between striations and growth lines, if they have 



