Prosser — Hamilton and Chemung Series. 



159 



3. Spirifer mesacostaHs, Hall. (c) 



One ventral impression distinctly shows the median plication 

 which is supposed to define this species. Another specimen is 

 almost the same as figure 3, plate XL, Pal. IV., except that it shows 

 a distinct sinus on the fold. This form was originally described as 

 S. acuminata which, in Vol. VIII., II. is stated to be probably 

 S. mucronatus (Con.), Bill., var. posterus, H. and C. It it pos- 

 sible that some of these specimens belong to this species, but they 

 all clearly show a sinus on the fold, or fold in the sinus, which is 

 characteristic of S. mesacostaHs. 



4. Ambocoelia umbonata (Con.), Hall. (c) 



5. Clionetes setigera, Hall (?). (r) 

 (I. Microdon (Cypricardelld) gregarius, Hall. (c) 



XLII B*. Exposures in the cuts along the Delaware and Hudson 

 railroad, 175 feet above the river level. The rocks are mostly olive shales, 

 but there are some of a bluish color that are iron stained and these contain 

 most of the fossils; interbedded are thin shaly sandstones. MhynchoneUa 

 (Camarotozehid) Stevensi, Hall; Spirifer mesacostaHs, Hall, and Microdon 

 (Cypricardelld) gregarius, Hall, are the most common species. The list is as 

 follows : 



1. JZhynchonella (Camarotcechid) Stevensi (H.), Hall and Clarke, (a) 



Some of the specimens may be compared with R. eximia (H.), 

 H. and C, as they are broad and similar in outline. 



2. Spirifer mesacostaHs, Hall. (a) 



The impressions of two ventral valves show very distinctly the 

 median septum in the sinus. 



3. Spirifer mesast/rialis, Hall (?). (rr) 



A large specimen with twenty or more plications on each side 

 of the sinus. 



4 Ambocoelia umbonata (Con.), Hall. (rr) 



5. Clionetes setigera, Hall. (rr) 



6. Microdon (Cypricardelld) gregarius, Hall. (a) 



7. Microdon (Cypricardelld) complanatus, Hall (?). (r) 



A few specimens are not dissimilar to figure 23, plate LXXIII 

 (Palaeontology of New York, loc. cit.), of M. ten// /'striata and 

 perhaps should be referred to that species. 



8. Orthoceras, sp. (fragments). (it) 



