74 CEPHALOPODA. 



Genus 26.— LITUOLA Lamarck. 



Generic Character. — Shell multilocular, partially spiral 

 and discoid ; volutions contiguous, the last terminating in a 

 straight line ; chambers irregular ; septa simple and trans- 

 verse, the last one perforated with from three to six orifices. 



Lituolites nautiloides. — The Nautilus-shaped Litu- 

 OLA. Plate X. fig. 22. Discoid, tailed, ribbed ; septa with 

 six perforations. Fossil at Mendon. 



Genus 27 SPIROLINA — Lamarck. 



Generic Character. — Shell multilocular, partly spiral and 

 discoid ; volutions contiguous, the last one terminating in a 

 straight line ; septa straight, perforated by a tube. 



Spirolina clavata. — The Club-shaped Spirolina. 

 Plate X. fig. 23. Club-shaped, spiral, smooth, ending in a 

 lengthened erect body. Fossil. 



Genus 28 SPIRULA Lamarck. 



Generic Character — Shell cylindrical, thin, subpellucid, 

 multilocular, spiral, discoid ; the volutions apart, mth a 

 straightish termination ; septa transverse, and equidistant, 

 externally concave, with an interrupted lateral siphon; aper- 

 ture round. 



Spirula Peronii. — Peron's Spirula. Plate X. fig. 24. 



White; very fragile, involute; diameter about one inch. 



Inhabits the West Indian seas. 



Lamarck has ascertained that the animal is cephalopodous, and 

 furnished with a sac, which envelopes the hind part of its body, at 

 which is seen the sheU, having only a portion of its last turn exposed. 



FAMILY VII. ORTHOCERATA. 



Shell straight, or nearly so, without any spiral volutions. 



Genus 29.— CONILITES.— ZamarcA. 

 Generic Character. — Shell conical, straight, slightly in- 



