70 



Descriptions of New Species of Fossils 



versely subcentral, distant from the concave margin about one-third 

 of the longitudinal diameter. Lower or ventral valve not observed. 



Surface marked by very fine, sharp, lamellose, concentric striae. 

 Entire surface minutely papillose. Shell ornamented with irrregular, 

 interrupted radiating lines or ridges of small, short, tubular spines, 

 diverging from the apex to the margins, and increasing in number 

 by implantation only. These radiating lines are composed of a single 

 row of imbricating spines forming a nearly continuous nodose 

 ridge. The specimen described has over thirty of these rows at the 

 margin. 



When in a perfect condition the spines do not show their tubular 

 character, being closed at the extremities. The individual is attached 

 to the dorsal valve of Rhynchonella StricJda)idi, and exhibits the 

 plications of that shell continued over the Ceaxia in corresponding 

 folds irrespective of the surface ornaments. 



From- G. setifera and C. Siluriaiia, with which it is associated, 

 and from any other palaeozoic form with which I am acquainted, this 

 species is distinguished by the radiating rows of spines. 



Orthis subnodosa n. s^). 



Ventral valve suborbicular, length and width about as 10 to 14 ; 

 hinge-line much shorter than the width of the shell ; an undefined 

 mesial depression on the lower half of the shell ; umbo prominent, 

 beak small and slightly incurved ; area small, triangular, apparently 

 not occuping more than half the width of the valve ; foramen large, 

 reaching to the beak, wider than high. 



Surface marked by subangular plications of which there are three 

 in the mesial depression, the central one being interstitial, coming 

 in below the umbo. There are about ten plications on each side of 

 the mesial depression, some of these coming from bifurcation or in- 

 terstitial additions ; the plications are crossed by lamellose lines of 

 growth, which give them a subnodose aspect. 



This species resembles, in some of its features, the 0. Jissicosta of 

 the Hudson river group. 



Ztgospiea minima n. sp. 



A small subglobose form, about as long as wide. Ventral valve 

 extremely gibbous, with a slight emargination in front. Dorsal 

 valve gibbous on the umbo, depressed in the middle, and concave 



