MARCELLUS LIMESTONES OF LANCASTER 161 



this point. I leng-th 7.4 mm, widtli 8.6 mm, truncation 1.5 mm; 

 II length 9.8 mm, width 12 mm, truncation 1.1 mm; IV length 

 9.4 mm, width 12 mm, truncation 1.2 mm. 



The species is rare in beds III and Y, only a few fragments 

 having been found. 



PRODUCTELLA Hall 



Productella spinulicosta Hall 



Pal. N. Y. 4:160, pi. 23 



In beds YI, YII, and YIII, specimens occur, which differ from 



Strophalosia truncata only in their greater size and 



the absence of truncation of the pedicle valye. These have 



since been referred to Productella by Hall and Clarke,^ " the 



existence of an articular system and of cardinal areas is not 



sufficient of itself to distinguish Strophalosia from Productella, 



and it will therefore be necessary to base distinctive generic value 



on the umbonal attachment of the former." Neither cardinal 



areas nor articular system has been observed in any of these 



specimens. 



Productella dumosa Hall 



Pal. N. Y. 4:162, pi. 23 



This species is rare in beds II and lY. The shell is preserved 

 on all the specimens, and the costae which form the spine bases 

 are slightly farther apart than on specimens from the Hamilton 

 shales. The largest specimen found has a length of 16 mm. The 

 width could not be measured. 



RHiPiDOMELLA Oehlert 

 Rhipidomella vanuxemi (Hall) 



Pal. N. Y. 4:47, pi. 6 



The species is represented by a few specimens in bed YII. 

 The shell is retained in a fairly perfect condition. The speci- 

 mens are all pedicle valves usually showing the exterior, but one 

 shows the interior with the large muscular scars and finely 

 striated margin of the shell. One specimen is 15.5 mm long and 

 18 mm wide, but the others found are much smaller. 



Pal. N. Y. vol. 8, pt 1, p. 315, 



