192 MANUAL OF THE MOLLUSCA. 
stationed on Drummond Island. Specimens haye also been 
brought home by the officers of many of the Arctic expeditions. 
But with the exception of one formerly in the possession of 
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Fig. 56. Huronia vertebralis.* 
jieutenant Gibson, and another in the cabinet of Mr. Stokes, 
the siphuncle 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 (Conotubularia, Troost). Shell extremely 
elongated, cylindrical. Siphuncle 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? O. bisipho- 
natum Sby, Caradoc sandstone, Brit. | 
‘‘Orthocerata with two siphuncles haye been observed, but 
there has always appeared something doubtful about them. 
In the present instance, however, this structure cannot be 
questioned.” (J. Sowerby.) 
Small orthocerata of various species are frequently found in 
the body chamber and open siphuncle of large specimens.t The 
endoceras gemelliparum and proteiforme of Hall, appear to be 
examples of this kind. 
6. Tritoceras= Diploceras, Salter. The shell is supposed to 
* Fig. 56. Huronia vertebralis, Stokes. 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.” 6 repre- 
sents a weathered section, presented to the British Museum by Captain Kellett and 
Lieutenant Wood, of H.M.S. Pandora. The figures are reduced 3. 
7 Shells of Bellerophon and Murchisonia are found under the same circumstances. 
