REPORT OF THE STATE PALEONTOLOGIST 1901 607 



Eunoa accola sp. nov. 



Shells of large size, outline normally subcircular or trans- 

 versely subelliptic; under compression appearing somewhat 

 squared by abrupt curves at the side. Brachial valve with low 

 radial lines diverging forward from the apex and seen best 

 when the test is slightly exfoliated. These are evidently, in 

 part at least, traces of muscular scars similar to such as are 

 frequently displayed by species of the genus Orbiculoidea. The 

 shell around the apex may have been continuous, but some 

 specimens indicate an obscure and short peripheral notch or 

 incurvature on the posterior edge. 



In the pedicle valve the cleft is wide, and its apex nearly 

 central. The edges of this cleft show convergent, thickened 

 shell ridges, which lie just within the margins and unite at some 

 distance in front of the apex, becoming thicker and more highly 

 raised, thence continuing forward for a short distance as a 

 single ridge, which soon fades out on the pallial surface. In 

 the existence of these muscular fulcra we find again a parallel 

 condition to that seen in many orbiculoids. 



The shell substance is highly tenuous but seems to show a 

 subdivision into two layers. Doubtless here, as in the cases of 

 such brachiopods elsewhere observed in bituminous shales, the 

 original lime content of the shell has been lost in fossiliza- 

 tion; however, this lime content must have been slight and 

 greatly subordinate to the phosphatic element. 



These shells are all large, indeed the species is one of the 

 largest of the inarticulate brachiopods. On bringing this genus 

 into comparison with known allied genera, we observe that its 

 differentials from those are as follows. 



In Orbiculoidea, the wide open pedicle cleft is an embry- 

 onal and nepionic condition in all species where the ontogenic 

 development has progressed normally. In Schizocrania it 

 is a normal adult phase, but Trematis is a heavier lime-shelled 

 genus with other differentials expressed in the submar- 

 ginal apex of the brachial valve and in the ornament of the sur- 

 face. Trematis likewise maintains the open foramina! fissure 



