No. 109.] , 171 



PRODUCTI OF THE HAMILTON AND CHExMUNG GROUPS. 



The number of species of Phodi ctus in tlie shales and shal}- 

 sandstones of the Hamilton and Chemung groups is greater than 

 usually supposed. The following, with one or two exceptions, 

 have been in my collection for many years, awaiting the com- 

 pletion of the fourth volume of the Palaeontology of New- York. 

 Among these are several forms which have externally the charac- 

 ters of Strophalosia ; but I have been unable to discover any 

 cardinal area in any of them, while in several species it is quite 

 certain that no such area could have existed. Several of these 

 species have a wide geographical distribution, but tlie larger 

 number are very restricted in their range so far as at present 

 known. 



These forms are interesting, as being the earliest representatives 

 of that type of Brachiopoda which so peculiarly marks the Car- 

 boniferous period; and we shall pi'obably yet find that the num])er 

 of species marking each of these groups is scarcely less than 

 the number marking each of tie subordinate divisions of the 

 Carboniferous limestone. 



Productus trUxVCatus (n. f^.). 



Pal. X.Y. Vol. iv. 



Shell small ; hinge-line usually equalling the greatest width of 

 the shell : dorsal valve concave near the margin, elevated in 

 the middle, and abruptly depressed or truncate towards the 

 beak : ventral valve ventricose, most elevated just below 

 the umbo, and sloping abruptly to the front; beak incurved, 

 truncate (often impressed) at the extremity; margin near the 

 hinge marked by a few strong wrinkles gradually becoming 

 obsolete on the body of the shell, which is crossed by undu- 

 lating stride of growth, and sometimes apparently with radiating 

 stri«. Surface ornamented with several interrupted rows of 



