EXPLANATION OF PLATE 42 



All figures approximately natural size 



Fig. 1. Astrodapsis whitneyi Bemond. A very characteristic species in the 

 lower part of the Upper Division of the San Pablo. A nteroposterior diameter, 

 60 mm. 



Fig. 2. Hytilus trampasensis, n. sp. An imperfect specimen of a left valve. 

 Longitude, 66 mm. 



Fig. 3. Mytilus trampasensis, n. sp. An imperfect specimen of a right valve, 

 showing shape of posterior end. 



Fig. 4. Modiolus direct us Dall. Longitude, 43 mm. 



Fig. 5. Mytilus perrini, n. sp. Always found associated with brackish water 

 species such as Cyrena (Corbicula) californica and Mya dickersoni. Longitude, 

 39 mm. 



Fig. 6. Mytilus perrini, n. sp. Longitude, 55 mm. 



[514] 



