Weller — Kinderhook Faunal Studies. 15 



Another change which took place during the life history of 

 this group of brachiopods was the reduction of the mesial sinus 

 in the pedicle valve. Among the Devonian representatives the 

 sinus was always present and sometimes it was developed to 

 an extreme degree, while in the latest representatives the 

 sinus is never conspicuous and is sometimes entirely obsolete. 



The Kinderhook representatives of this group of shells 

 exhibit, in general, an intermediate condition, and the North- 

 view specimens are no exception. The largest and best pre- 

 served specimen is 37 mm. in breadth and the sinus is but 

 moderately developed. It is referred to the Carboniferous 

 species S. swallovi or 8. resupinata^ although phylogeneti- 

 cally it is probably between that species and some of those of 

 Devonian age. Of the Devonian species it approaches most 

 closely to S, impressa of the Chemung, but the sinus in 

 S, impressa is on the average much more strongly developed 

 than in the Northview specimens. 



Rhipidomella burlingtonensis ( Hall ) . 



PI, iv.f.13. 



This species is present in almost every Kinderhook fauna, 

 and it is one of the commonest ones at Northview. It is 

 closely allied to the European R. michelini^ but a comparison 

 of American specimens from various localities and horizons 

 with European specimens and illustrations, seems to indicate 

 that the more prominent beak is a constant character of R. 

 burlingtonensis by which it may be separated from R, miche- 

 lini. The species is allied to the Devonian R. vanuxemi, 

 and it is entirely probable that the two forms are genetically 

 related. 



Chonetes ILLINOI8ENSIS Worthcu. 



PI. IV. f. 10, 



Chonetes multicosta Winchell, described from the " Yellow 

 Sandstone '' and '* the base of the Burlington limestone " at 

 Burlington, Iowa, is perhaps not distinguishable from O, 

 illinoisensis . It is described as having 180-200 radiating 

 costae, and two or three cardinal spines upon each side of the 

 beak nearly at right angles to the hinge-line, C, illinoisensis 

 on the other hand is described as having 100-120 or more 



