OBLiaUE. 205 



Nummulites, Siderolites, Vorticialis, Helicites, Orbiculina, Pla- 

 centula. 



NUMMULITES. Lam. (Nummus, money.) Fam. Nautilacea, Lam 

 — Descr. Orbicular, convolute, shewing no trace of spire externally; 

 interior divided into cells spirally arranged. — 06s. The singular 

 fossils composing this genus receive their name from their 

 external resemblance to a battered coin. Fig. 4/2. N. lenticulina. 



NUX. Humph. Cyclas, Lam. 



NYMPHACEA. Lam. A family belonging to the order Conchi- 

 fera Dimyaria, Lam. Ligament external, placed on a prominent 

 fulcrum. This family contains the following genera- 



1. Sangtjinolaria. Rostrated, gaping ; two cardinal teeth in 



each valve, including Soletellina and Lobaria. Fig. 98, 99. 



2. Psammobia. Quadrate; valves closed, including Psam- 



motsea. Fig. 100. 



3. Corbis. Thick, fimbriated ; a cardinal tooth in the centre 



of a pit. Fig. 101. 



4. Grateloupia. A series of small teeth filling a triangular 



area. Fig. 102. 



5. Egeria. One single and one double cardinal tooth. Fig. 



103. 



6. Lucina. Rounded ; anterior muscular impression tongue- 



shaped. Fig. 104. 

 7- Tellina. An anterior fold in the ventral margin ; lateral 

 teeth. Fig. 105, 106. 



8. Tellinides. No anterior fold ; no lateral teeth. Fig. 107. 



9. Don ax. Margin denticulated; shell wedge-shaped. Fig. 



108. 

 10. Capsa. Margin not denticulated, no lateral teeth. Fig. 109. 

 OBELISCUS. Humph. Trochus, Lam. 



OBLIQUE, (obliquus. lat.) In a slanting direction. The whorls 

 of spiral univalves generally take an oblique direction in reference 

 to the imaginary axis of the shell. A bivalve is said to be oblique 

 when it slants off from the umbones. An example of this is seen 

 in Avicula, fig. 163. 



