1913.] NATURAL SCIENCES OF PHILADELPHIA. 615 



form, but while the shell is heavy, it lacks the upturned edge of 

 0. antiguensis. Length 85 mm., alt. 80 mm., depth of lower valve 

 30 mm. Cotypes, A. N. S. P. Collection, invertebrate fossils, Nos. 

 1,653 and 1,655. 



In size and plication 0. antiguensis varies largely, but of the 

 specimens collected the longest shells do not run far from 90 mm. in 

 altitude. As regards plication, some are nearly smooth and some 

 are strongly rugose, even in some cases spinose, but all may be 

 distinguished by the broad furrow which runs across the exterior of 

 the lower valve about opposite to the muscle impression and which 

 divides the rugse into a group of five and one of two. The species 

 differs also from all other closely related American species by the 

 upturned margin of this lower valve and the correspondingly reflexed 

 margin of the upper or flat valve. 



Explanation of Plates XVIII, XIX, XX. 



Plate XVIII. — Fig. 1 . — Peden (Amusium) antiguensis n. sp. View of the exterior 

 of a silicified specimen, showing some of the original shell surface. Natural 

 size. 



Fig. 2.— Peden (Amusium.) antiguensis n. sp. Interior view of shell. Nat- 

 ural size. 



Fig. 3. — Peden {Amusium) antiguensis n. sp. Exterior, showing hinge, of a 

 non-silicified specimen, partly imbedded in the rock. Natural size. 



Fig. 4. — Peden {Chlamys) anguillensis Gupp3^ Exterior of a siUcified 

 specimen, in which the original surface was destroyed by the siUcification. 

 Natural size. 



Fig. .5. — Peden (Amusium) antiguensis n. sp. Detail of a portion of speci- 

 men 1. X 3. 



Fig. 6 — Peden (Chlamys) anguillensis Guppy. Exterior of an unsilicified 

 specimen, showing the distinctive secondary ribbing. Natural size. 



Fig. 7. — Peden (Chlamys) anguillensis Guppy. Interior of valve. Natural 

 size. 



Fig. 8— Peden (Chlamys) anguillensis Guppy. Exterior of a silicified 

 specimen, showing traces of the secondary ribbing. Natural size. 



Plate XIX. — Fig. 1. — Helicina crosbyi n. sp. Mouth view of a specimen. X 2. 

 Fig. 2. — Peden nugenti n. sp. Interior view of the shell, showing the hinge. 



Figure slightly above natural size. 

 Fig. 3. — Helicina crosbyi n. sp. Under side of shell, showing the heavy 



umbilical callus and thickened lip. X 2. 

 Fig. 4. — Orbitoides manteUi Mort. The figure shows a fragment of the rock 



with two specimens of this large species. About natural size. 

 Fig. 5. — Peden nugenti n. sp. Exterior aspect of the deeper valve. Very 



slightly enlarged. 

 Fig. 6. — Peden nugenti n. sp. Enlarged view of a fragment of the exterior 



of the shell, showing the concentric secondary sculpture. X 3. 

 Fig. 7. — Ostrea antiguensis n. sp. Interior of shell, showing muscle impres- 

 sion and hinge. Natural size. 

 Fig. 8. — Helicina crosbyi n. sp. Lateral view of shell, showing the raised 



and thickened outer part of the lip. X 2. 



Plate XX. — Fig. 1. — Ostrea antiguensis n. sp. Exterior of the deep valve of a 

 nearly smooth specimen. The figure is shghtly above the natural size. 

 Figs. 2-4. — Turritella forresli n. sp. X 3. 



