100 Mr. T. U. Jones on some specks of Leperditia. 



smaller individual; anterior and central tubercles distinct, but 

 radiating vessels only apparent towards the ventral border ; b, the 

 same, ventral aspect, with a part of the inverted edge remaining 

 attached ; c, the same, dorsal aspect. — Museum of the Geological 

 Society. 



Fiff. 6. Leperditia Britannica'i : a, right valve ; b, the same, ventral aspect ; 

 c, the same, anterior aspect. The dotted line indicates the 

 supposed outline of the opposite valve. — Mr. Morris's Cabinet. 



Fig. 7. Leperditia Britannic a, transverse vertical section of the carapace, 

 after Rouault (Bull. Soc. Geol. Fr. 2 ser. vol. viii. p. 378. fig. 3). 



Plate VII. 



[The figures represent the specimens magnified two diameters, excepting 

 figs. 4 d and 5, which are more highly magnified.] 



Fig, 1 a. Leperditia Arctica, right valve ; central and anterior tubercles well 

 developed, the latter ornamented with an oval crenulated border. 

 — Museum of Practical Geology. 



F^g. I b. Leperditia Arctica, right valve, anterior extremity. — Museum of 

 Practical Geology. 



Fig, 2. Leperditia Arctica : a, left valve ; &, the same, anterior extremity. 

 — Museum of Practical Geology. 



Fig, 3. Leperditia Arctica : a, perfect carapace, showing the right valve ; 

 b, the same, showing the left valve ; where the carapace is broken, 

 the radiating vessel-markings are seen; c, the same, dorsal 

 aspect ; d, the same, ventral aspect ; e, the same, anterior aspect. 

 — Museum of Practical Geology. 



F^g. 4. Leperditia Arctica : a, cast of the interior of a left valve; b, the 

 same, ventral aspect ; c, the same, anterior aspect ; the dotted 

 line indicates the outline of the opposite valve in section ; d, en- 

 larged view of the cast of the central tubercle ; e, fragment of 

 the same left valve, showing the inner aspect of the "central 

 tubercle," or " lucid spot," and the vascular markings, together 

 with a portion of the inverted edge of the same valve ; the lower 

 fragment is a portion of the overlapping edge of the right valve. 

 — Museum of Practical Geology. 



Fig. 5. Leperditia Arctica : diagram showing the relations of the over- 

 lapping and overlapped ventral edges of the valves. 



Fig. 6. Leperditia altal : a, right valve, with weather-worn surface; 6, the 

 same, ventral aspect ; c, the same, anterior aspect. — Museum of 

 Practical Geology. 



Fig. 7- Leperditia alta? : a, left valve (young), with weather-worn surface; 

 b, the same, ventral aspect; c, the same, anterior aspect. — 

 Museum of Practical Geology. 



Fig. 8. Leperditia gibbera : a, right valve, shell nearly all worn (or rather 

 dissolved) away ; b, the same, ventral aspect ; c, the same, an - 

 terior aspect. — Geological Society's Museum. 



Fig, 9. Leperditia gibbera : a, left valve, surface well preserved ; b, the 

 same, ventral aspect ; c, the same, anterior aspect. — Museum of 

 Practical Geology. 



Fig. 10. Leperditia gibbera, outline profile of the anterior aspect of the 

 carapace. 



Fig, 11. Leperditia marginatal (young?): a, cast of right valve; b, the 

 same, ventral aspect ; c, the same, anterior aspect. 



Fig, 12. Leperditia marginat a 1 (young?): a, cast of left valve ; 6, the same, 

 ventral aspect ; c, the same, anterior aspect. 



