NOTES ON PALEOZOIC CRUSTACEANS 109^^ 



presence serves to emphasize very materially the universality in 

 northern altitudes of Old Red conditions, during the period of 

 time represented by the deposition of the Oneonta-Oatskill sedi- 

 ments, a mass of sands and shales in part highly colored and 

 attaining a thickness of 3000 to 4000 feet. 



5 ESTHERIA ORTONI SP. NOV. 



PLATE 4, FIGURES 5-8 



Several years ago the late Prof. Edward Orton presented the 

 writer with a number of specimens of an E s t h e r i a from 

 the lower barren Coal measures of Carrollton (O.). The species 

 appears to have abounded in this argillaceous rock, where its 

 only organic associate among the specimens studied, is the 

 phyllopod Leaia tricarinata Meek and Worthen, and a 

 the figures we have given of the young stages of this shell, that 

 t h e r i a is worthy of note, among them being the character 

 of the umbo and hinge, and I have already given an illustration 

 of the species with considerable enlargement in Eastman-Zit- 

 tePs Textbook of paleontology (p. 640, fig. 1333) designed to show 

 the strong node which is present in the umbonal region. The 

 species is of small size; the specimens represent various growth 

 stages from a length of .5 to 1 mm, where but three to seven con- 

 centric growth lines are present in a length of 3 mm, in which 

 state the shell may have 20 concentric ridges. The relatively large 

 size of these ridges and the distance between them are very 

 striking in young stages, and it appears on comparison of such 

 stages with the mature phase of the species that this early con- 

 dition is to some degree at least obliterated at maturity in the 

 progress of successive molts. It will be observed, on consulting 

 the figures we have given of the young stages of this shell, that 

 the primitive umbo is broad and quite bare, not being raised to 

 an apex or beak but being surmounted by a sharply defined 

 elongate, muscular node. Except for this node the aspect of 

 these small shells, with bare umbonal region and sloping round- 

 shouldered valves, is much more like that which prevails in the 

 living genus L i m n a d i a than in either recent E s t h e r i a 



