318 PALAEONTOLOGY OF NEW YORK. 



The two species named are large, ponderous shells, having the cardinal area and 

 teeth conspicuously developed, the external surface covered with fine radiating 

 striai, and devoid of spines The existence of the secondary muscular scar in 

 the pedicle-valve can hardly be regarded as a distinctive feature, since it is also 

 well defined in some other species of Productus. The form and size of the 

 shells, the arrangement of the muscular scars, and their dendritic markings, 

 and the structure of the cardinal process, all show the very close relationship 

 of these species to the typical forms of Proddctus. It will be difficult to find 

 features of intrinsic importance upon which to justify the separation of these 

 fossils from Productella, unless it be in the spineless surface ; and yet the 

 general form and expression of the shells is so different from what we are 

 accustomed to meet with in that distinctively Devonian genus, that for the sake 

 of homogeneity in the grouping, it may be well to retain for them this desig- 

 nation. 



Both P. Llangollensis and P. comoides are from the Welsh Coal Measures, and 

 may be regarded as the final expression of that combination of characters con- 

 stituting Productella in earlier faunas. 



