Mr. J. S. Miller on Belemnites. 47 



At length the Belemnite was considered to be the remains of a testaceous 

 animal^ and a new series of theories and conjectures arose. The form and ca- 

 vity then afforded grounds for referring it to the genus Dentahum. 



The concave septa induced Von Tressau to consider it as a limpet. 



Klein in his Descriptiones Tubulorum Marinorum, published at Dantzic in 

 1731 J appears to be one of the first writers* who entertained clear notions of 

 its nature. His generic description is as follows : " Tubulus marinus fossilis^ 

 materiaeatseleniticamaccedentis; teres; transversim fractus concentricis striis, 

 in longitudinem fissus canaliculo pervio semper in medio posito donatus ; in 

 basi nonnunquam fovens conum ohm testaceum concameratum_, instructum 

 siphunculo." 



Breyniusf, Da Costa^ and Brander J added but little to the observations of 

 Klein. 



Plottj in the Philosophical Transactions for 1764^ considerably extends our 

 knowledge of the structure of the Belemnite^, though an ignorance of the true 

 nature of the moUuscEe inhabiting the chambered univalves has led him to main- 

 tain several erroneous opinions with regard to the exact mode of its formation. 

 He observes that the concave septa in the superior conical shell were connected 

 by a siphuncle, and suggests that the animal lived in its outer chamber : he 

 also considers the sheilas having sustained nochange^ and proves this from the 

 vestiges of its laminar construction^ which he compares to that of the oyster. 

 Yet Plott does not agree with Dr. Hooke, that the siphuncle extends through 

 all the chambers ; and gives a rather unsatisfactory account of the manner in 

 which the animal is, according to his hypothesis,, to leave the aperture of its 

 first chamber without separating from the siphuncle, and to assume a figure 

 which may permit it to crawl on the bottom of the sea and to drag its shell with 

 it. He states that the animal, both on its return and in its progress, clasps 

 the whole guard by two flaps or sides of its mantle, as a snail does a small 

 branch of a tree, and that in so doing it deposits by excretion the lamellse 

 Avhich form the guard (in a manner very similar to that in which the Cyprsa 

 increases its shell). The sulcus, which may be observed traversing the sur- 

 face of the Belemnite longitudinally, he considers as indicating the interval in 

 which the two flaps of the mantle must have met in thus clasping the guard. 



As the chambered portion of the Belemnite is so closely analogous to the 

 shell of the Nautilus, — Walch, Parkinson, and Lamarck agree in the opinion 

 that, hke that shell, it was destined to aid the buoyancy of its inhabitant : but 



* Rosinus perhaps at an earlier time had published ideas corresponding with those of Kl-ein, 

 but I have no opportunity of referring to his work, 

 t Dissertatio de Polythalamiis. 

 X Phil. Trans. 



