112 



tiulosus, N. legumen, and N. raphanus. But, obliged to observe certam 

 limits, I shall not dwell, in this work, on those fossils which are so small 

 as to be microscopic objects, except where it is required, for the sake of 

 particular illustration. 



In reviewing the history of these fossils, we find many instances of 

 the perplexity and confusion proceeding from an endeavour to ascertain 

 the nature of a body, which cannot be referred to any known recent 

 animal, as strictly analagous. Gesner. de Figuris Lapidum, cap. xiv. p. 167, 

 and Aldrovandus, Museum Mctallicum, pag. 732, considered them as the 

 petrified tails of crabs; the former naming them Cauda cancri, s, astaci fluvia- 

 tilis ; and the latter, Cancrita. But as the knowledge of fossils advanced, 

 their resemblance to the alveolus of the belemnite was perceived, and they 

 were considered by many as the alveoli .of large belemnites, and there- 

 fore obtained the name of cylindrical alveoli. Some of these fossils were 

 even considered as part of the vertebral spine of some marine animal : 

 an excuse for which may be found in the particular forms possessed by 

 some of these bodies. Our countryman, Lhwydd, did not make much 

 progress in developing the nature of these fossils; he was satisfied with 

 naming them Alveoli; and, of course, with considering them as the 

 alveoli of large belemnites. 



Scheuchzer, although not informed of the real nature of these fossils, 

 very properly separated them from the belemnites. No correct know- 

 ledge, however, was obtained respecting them, until Breyn and Klein 

 made them the objects of their investigations, and were led to the con- 

 clusion, that they were the remains of some marine, univalve, cham- 

 bered shell. This opinion was soon confirmed by the discovery, by 

 Plancus, of minute recent shells on the shores of Rimini, which appeared 

 to possess the characters of orthoceratites: but no recent shells of this genus 

 are known, except those which have been found in the sea sand of dif- 

 ferent parts, and which are so minute,' as to be microscopic objects. 



The shells of this genus, Plate VII. Fig. 14, like the nautili, are 

 divided into chambers by septa, through which passes a tube or siphun- 



