1912.] NATURAL SCIENCES OF PHILADELPHIA. 519 



Length of right valve 18.7, alt. 11, diameter 4.8 mm. 



Gatun Formation, from the excavation at the lower locks at Gatun. 



This species has much in common with such species of the sub- 

 genus Bothrocorbula as C. viminea Guppy and C. radiatula Dall, 

 and C. synarmostes Dall, but the total absence of any trace of a 

 lunular pit at once distinguishes the Gatun form. The small 

 number of concentric waves of the exterior separates C. hexacyma 

 from various species of Cuneocorbula, which otherwise resemble it 

 more or less. 



Explanation of Plates XXII-XXVI. 



Plate XXII. — Figs. 1-3. — Callianassa scotli n. sp. 



Fig. 4. — Pleurotoma (Gemmula) vaningeni n. sp. X 3. 



Fig. 5. — Fasciolaria gorgasiana n. sp. X 3. 



Figs. 6, 7. — Nassa (Hima) prceambigua n. sp. X 4. 



Fig. 8. — Pyrula micronematica n. sp. X 2.5. 



Fig. 9. — Natica bolus n. sp. X 3. 



Fig. 10. — Natica canalizonalis n. sp. X 3.5. 



Figs. 11, 12. — Bittium scotti n. sp. X 3.5. 



Fig. IS.—Sigarelus Eunaticina) gabbi n. sp. X 3.5. 



Plate XXIII. — Fig. 1. — Pecten (Amusium) luna n. sp. 



Fig. 2. — Pecten oxygonum optimum n. subsp. (Costa Rica). 



Fig. 3. — Pecten oxygonum canalis n. subsp. 



Fig. 4. — Area dalli n. sp. 



Fig. 5. — Crassatellites reevei Gabb. 



Fig. 6. — Cardium (Trachycardium) durum n. sp. 



Plate XXIV. — -Figs. 1, 2. — Pecten (Amusium) sol n. sp. 



Fig. 3. — Pecten (Euvola) reliquus n. sp. detail of sculpture. 



Plate XXV. — Figs. 1, 2. — Sporulylus scotti n. sp. 



Figs. 3, 4. — Crassatellites mediamericanus n. sp. (Costa Rica). 

 Fig. 5. — Crassatellites mediamericanus n. sp. 'Pecten Bed, Las Cascades, 

 C. Z. 



Plate XXVI. — Fig. 1. — Dosinia delicatissima n. sp. 

 Fig. 2. — Petricoli millestriata n. sp. 

 Fig. 3. — Thracia (Cyathodonta) gatunensis Toula. 

 Fig. 4. — Corbula (Cuneocorbula) hexacyma n. sp. 

 . Fig. 5. — Tellina cequiterminata n. sp. 

 Fig. 6. — Tellina (Eurytellina) vetula n. sp. 



34 



