PLATE XXIII. 



Pentaceros Boysii, Forbes, sp. (Page 80.) 



From the Upper Chalk. 



Fig. 



1. Snpero-marginal plate; magnified 4 diameters. (Coll. Brit. Mus., 48083.) 



a. Lateral view of extremity of arm from which the above snpero-marginal plate 



was drawn ; natural size. 



b. Dorsal view of extremity of same arm ; natural size. 



Pentacekos bulbifeeus, Forbes, sp. (Page 77.) 

 From the Tapper Challi. 



2. Abactinal aspect ; natural size. (Coll. Brit. Mus., E. 5042.) 



a. Madreporite; magnified 5 diameters. 



Pentaceros bispinosus, n. sp. (Page 87.) 

 From the Upper Chalk. 



3. Actinal aspect ; natural size. (Coll. Brit. Mus., 35482.) 

 ft. Actinal view of extremity of arm ; natural size. 



b. Infero-marginal plate ; magnified 3 diameters. 



c. Ventro-lateral plate ; magnified 4 diameters. 



