112 INTRODUCTION. 



of the shell. ^ M. Bouchard is of opinion that Davidsonia forms the passage from the 

 articulated to the unarticulated genera. M. de Koninck considers it to bear more analogy 

 to Thecidea than to any other,^ while Professor King and Mr. Woodward would place the 

 genus in the family Strophovienida . 



Geol. range. — In our present knowledge the genus is limited to the Devonian epoch. 

 It occurs both at Chimay, and in the Eifel ; in that horizon characterised by the Calceola 

 sandalina. 



Examples : D. Verneuili, Bouch. ; D. Bouchardiana, De Koninck. 



Family— PRODUCTID^. 



Animal unknown ; Shell entirely free, or attached to marine bottoms by the sub- 

 stance of the beak ; valves either regularly articulated or kept in place by muscular action ; 

 no calcified supports for the oral appendages, which were no doubt fleshy and spirally 

 rolled. 



Obs. We have admitted into this family the following genera : Ckonetes, Strophalosia, 

 Aulosteges and Productus, on account of the natural and intimate relation they bear to 

 each other, as may be better understood by a glance at their respective figures (Pis. 

 VIII and IX.) In all we perceive the same dispositions of the muscular system,^ the same 

 reniform impressions (supposed to be vascular ?) and the same elevation on each side of 

 the cardinal ridge (marked g' in PI. IX, fig. 214, 219, &c.) In all, the surface of the 

 valves is ornamented by tubular spines, which only vary in position and abundance. 

 Professor M'Coy removes Chonetes, Strophalosia, and Aidosteges from the Production,* 

 and places them among the Strophomenidn or LEPT^NiDiE ; but we regret not being 



1 M. Deshayes, Professor King, and Mr. Woodward, also believe that the form of the cones is due to 

 the influence of the free arms upon the mantle lining the inner surface of the shell. M. de Koninck was 

 correct in stating that the pallial vessels had left impressions on the outer sides of the cones and margins 

 of the shell ; but I was further able to trace the principal vascular trunks, from their origin between the 

 muscles to near the front of the shell, where sweeping sub -marginally round both sides of the mantle 

 they give off bifurcated veins, which have left impressions on the frontal and latei-al margins of the 

 cones, in a somewhat similar manner to what we find so well illustrated in Professor King's figures 

 of Stroph. analoga (' Mon. of English Permian Fossils,' pi. xx, figs. 6 and 7). 



2 I admit, with M. de Koninck, that the external shape of Davidsonia is very similar to that of 

 certain Thecidia, such as Th. Moorei and Bouchardii, but as the Belgian author justly observes, the 

 internal dispositions are very different from those seen in any species of Defrance's genus Thecidiiim. 



^ Professor M'Coy is mistaken when he states that no traces of the dendritic muscular impressions 

 are visible in Strophalosia or Aulosteges : — I have distinctly observed them in both. I must also confess I 

 see a great difference between the reniform impressions of Productus Strophalosia, &c., and the vascular 

 system of Leptcena transversalis. 



* British Pal. Fossils in the Mus. of Cambridge, p. 387, 1852. 



