192 



MANTJAL OP THE MOLLTJSCA. 



Btationed on Drunmiond Island. Specimens have also been 

 brougb.t bonie by the officers of many of the Arctic exj)editions. 

 But with the exception of one formerly in the possession of 



Fig. 56. Iluronia vertebralis.* 



liieutenant Gibson, and another in the cabinet of Mr. Stokes, 

 the siphnncle only is preserved, and not a trace remains of septa 

 or shell wall. Some of those seen by Dr. Bigsby in the lime- 

 stone cliffs were 6 feet in length. 



5. Endoceras, Hall (Conotubnlaria, Troost). Shell extremely 

 elongated, cylindrical. Siphnncle very large, cylindrical, lateral ; 

 thickened internally by repeated layers of shell, or partitioned 

 off by funnel-shaped diaphragms. 12 species. Lower Silurian, 

 New York. 



Shell perforated by two distinct siphuncles ? 0. bisipho- 

 natum Sby, Caradoc sandstone, Brit. 



" Orthocerata with two siphuncles have been observed, but 

 there has always appeared something doubtful about them. 

 In the present instance, however, this structure cannot bo 

 questioned." (J. Sowerby.) 



Small orthocerata of various species are frequently found in 

 the body chamber and open siphnncle of largo specimens, f The 

 endoceras gemeUiparurn and proteiforme of Hall, appear to be 

 examples of this kind. 



6. Tritoceras = Diploceras, Salter. The shell is supposed to 



* Fig. 56. Huronia vertehralis, Stokca. a from a specimen in the British Museum 

 presented by Dr. Bigsby. The septa are added from Dr. Bigsby's drawing ; they were 

 only indicated in the specimen by " colourless lines on the brown limestone." b repre- 

 sents a weathered section, presented to the British Museum by Captain Kellett and 

 Lieutenant Wood, of H.M.S. Pandora. The figui-es are reduced ^. 



t Sheila of Belleroj}/w7i and Murchisonia axe found under the same circumstances. 



