PLATE I. 

 Uraster Gaveyi, Forbes. 



From the Middle Lias, 



Fig. 



1 a. Uraster Gaveyi, Forb., p. ]00. Under surface, natural size. 



b. Plan of the ambulacral plates and their spiny borders. 



2 a. Portion of the dorsal surface of a ray of Uraster tenuispinus, M. and T., to show the 



spines and pores in the tegumentary membrane. 

 b. Portion of the ventral surface of the same ray, to show the biserial arrangement of the 

 tentacula in the ambulacral valley with the lateral spines bounding the 

 the same. 



3. Diagram of the ambulacral plates in Uraster rubens, Lin., for the purpose of com- 

 paring them with the homologous parts in the Possil species figured in 

 the same plate. 



