PLATE XVIII. 



Holectgpi from the Inferior Oolite and Cornbrash. 



Fig. 



1 a. Holectypus depressus, Leske, p. 260. Upper surface, natural size. 



b. The base, showing the mouth and anal openings, natural size. 



c. A side view of the same test, natural size. 



d. Ambulacral areas, poriferous zones, and inter-ambulacral plates, magnified three 



diameters. 



e. Primary tubercle from the upper surface, with its circle of areolar granules, magnified 



seven times. 

 /. Primary tubercle from the base, magnified seven times. 

 g. Under surface of another specimen, showing the jaws in situ, natural size. 

 h. Portion of a primary spine, magnified eight times. 

 i. The apical disc, magnified three and a half times. 



2 a. Holectypus' hemisph^ericus, Agassiz, p. 264. Upper surface, natural size. 



b. Under surface, natural size. 



c. Posterior view, showing the marginal anal opening. 



d. Ambulacral area, poriferous zones, and three inter-ambulacral plates, magnified three 



diameters. 



e. The apical disc, magnified three times. 



/. Lateral view, showing the greater length of the posterior half. 



g. A conical variety, showing the height of the pyriform marginal anal opening. 



h. The base of a large specimen. 



Holectypus from the Coral Bag. 



3 a. Holectypus oblongus, Wright, p. 267. Upper surface, natural size. 



b. Base of a small specimen, natural size. 



c. Lateral view of a, natural size. 



d. Ambulacral area, poriferous zones, and two inter-ambulacral plates, magnified four 



diameters. 



