Maryland Geological Survey 421 



The forms found are all small. The ovate triangular outline, con- 

 spicuous concentric subimbricating striiv, and plications distinguish it 

 from Spirifer modestus. It differs from Spirifer crispus of the Niagara 

 in its fewer and less marked plications. 



Length 13 mm. ; width 14 mm^. 



Occurrence. — Helderberg Formation, Keyser Member. Eoundtop.' 



Collection. — Maryland Geological Survey. 



[Maynard.] 



Genus AMBOCCELIA Hall = 

 Amboco^lia umbonata (Conrad) ? 



Orthis umbonata Conrad, 1842, Jour. Acad. Nat. Sci. Phila., vol. viii, p. 264, 



pi. xiv, fig. 4. 

 Ambocfclia umhonata Hall, 18G7, Nat. Hist. N. Y., Pal., vol. iv, p. 259, pi. xliv, 



figs. 7-18. 



Description. — The Maryland Helderberg material referred with some 

 doubt to this species, and which is not well preserved, is indistinguishable 

 from Hamilton specimens except in size, being less than half that of the 

 latter. The writer would not make this identification and thus give A. 

 umhonaia a range from late New Scotland into the Chemung, were it not 

 that he has this species from the Upper Oriskany of Armuchee Creek, 

 northeast end of Lavender Mountain, Floyd County, Georgia. When 

 better material is at hand, the Helderberg specimens may prove to be dis- 

 tinct. 



As these pages are printing Clarke's Early Devonic History of New 

 York and Eastern North America (Memoir 9, pt. 1, N. Y. State Mus., 

 1908, p. 182) comes to hand. From it we see that probably this same shell 

 occurs at Gaspe, Canada. Clarke names it Spirifer modestus nitidulus and 

 states that S. modestus " expresses in its outward form and characters the 

 Tisual features of the Middle Devonic genus Ajnbocoslia save for the 

 greater convexity of the dorsal valve. Amboccelia unquestionably belongs 

 in this category but has certain differentials in the arrangement of the 



' It is possible that this species is from the Tonoloway formation. 

 - For a.revised description of this genus, see Hall and Clarke, Nat. Hist. N. Y., 

 Pal., vol. viii, 1893, pt. ii, pp. 54-56. 



