MOLLUSCA. 
385 
TRIBE VI.-LITUOLACEA. 
Shell somewhat spiral; the last volution continuous in a 
straight line. 
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 transverse, the last 
one perforated with from three to six orifices. 
Lituolites nautiloidea. — The Nautilus-Shaped Lituola. 
Plate LXXXIII. 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 LXXXIII. fig. 23. 
Club-shaped, spiral, smooth, ending in a lengthened erect body. 
Fossil. 
Genus 28.—SPIRULA.— Lamarck. 
Generic Character .—Shell even, thin, subpellucid, multilocu¬ 
lar, spiral, discoid; the volutions apart with a straight termina¬ 
tion ; septa transverse, and equidistant, externally concave, with 
an interrupted lateral syphon ; aperture round. 
Spirula Peronii.— Peron’s Spirula. 
Plate LXXXIII. fig. 24. 
Pale sulphur-yellow, very fragile, horn-shaped; diameter 
about one inch. Inhabits the West Indian seas. 
TRIBE VII.-ORTHOCERATA. 
Shell straight, or nearly so; without any spiral volutions. 
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