P»Li>LTE VIII. 



Pnge. 



Fig. 1. Spiiui-f.kix A I'l-i.citnA S5 



1. Doi's:il viow of tbc origiual typical spccinu-n. 



la. Veutrul view of same. 



1 h. An ontliiio profile of same. 



1 c. All internal cast of the ventral valve, showing the slit left by the rostral septiiiii. 



1 d. A (liii'sal view of another very gibbons specimen. 

 ) e. An ontliue profile of same. 



Fig. 2. PitoDicTis Nevadrnsis C4 



'2. Ventral view of a specimen, with the ears broken away. 

 i a. Cast of the exterior of a ventral valve of same species. 



2 6. Ventral aspect of another specimen, turned so as to give a more direct view than 



fig. 2. 

 2 c. Internal cast of ventral valve. 

 2rf. Aside view of same. 



2 f . A longitudinal section of a specimen with the valves united. 



Fig. ;i. Pi!<)t>t;cTrs multistri atus 76 



3. Ventral view of a rather large specimen, with the free margins broken away. 

 'ia. Side view of same. 



3 6. Ventral view of a smaller specimen, with one ear and much of the margins broken 



away. 



3 c. Dorsal view of last. 

 3d. Side view of same. 



3f. Internal view of a dorsal valve, too much worn to show internal markiugs, but 

 .showing the very abrupt geniculalion of the anteridr and lateral margins around 

 the flattened visceral regioti. 



Fig. 4. PnonucTus I-o.ngispinus "8 



4. A side view. 



4 a. Ventral view, with ears partly broken away. 



Fig. 5. .'^iMiaiERiXA (undt. sp.) B4 



r,. Dorsal view of a specimen, with lateral extremities imperfect. 

 .'> a. Autero-veutral aspect of sauio. 

 !■) 6. A side view of same. 



Fig. G. Aiiivius .sunriuTA 83 



ti. Dorsal view. 



iia. An outline prolili! of same. 



