398 Mr. A. H. Foord on " Orthoceras 



the diameter has increased to 19 lines. But on the whole the 

 septa increase their distance as the individual advances in 

 age. Siphuncle proportionately larger in the young than in 

 the adult, as is frequently the case in the testaceous Cepha- 

 lopods ; that is to say, it attains to nearly half the diameter in 

 the young shell (fig. 1, d), while in the adult it measures only 

 about one third of the diameter (fig. 1, c). Test consisting 

 apparently of two layers^ the inner one being perfectly smooth 

 and polished, whilst the outer, the surface of which is rarely 

 preserved, is ornamented with transverse, irregular, slightly 

 oblique riblets (fig. 1, h). 



Remarks. The ^''Orthoceras commune'''' of Boll (not Hi- 

 singer), which I believe to be identical with Endoceras 

 Wahlenhergi, is described by that author as having the " shell 

 in well-preserved examples marked with obscure lines of 

 growth, and in badly preserved ones these are so eroded that 

 their sculpture can scarcely be recognized ; " the latter is 

 unfortunately the condition of most of the specimens in the 

 National Collection. 



It has been a matter of great difficulty to me to select out 

 of the numerous and divergent forms described and figured 

 under the name of '' Orthoceras duplex " those whose 

 characters harmonized sufficiently with the species I have 

 now instituted, to justify their incorporation with it. The 

 descriptions of "0. duplex^'' have often been based upon 

 imperfect fragments, consisting of casts, or even of sections 

 only, of a few of the chambers, in which the distinguishing 

 characters are necessarily reduced to a minimum. In some 

 instances the siphuncle only has been figured. 



In such circumstances I cannot vouch for the accuracy of 

 all the references given above. The dubious ones are indi- 

 cated by a note of interrogation. 



Amongst the specimens of E. Wahlenbergi from Westro- 

 gothia two attain a considerable size, the longest measuring 

 1 foot 1\ inches, the diameter at the larger end being 2^ 

 inches and at the smaller end 10 lines. The other measures 



1 foot 5 inches in length, with a diameter of 2 inches and 8 

 lines at the larger extremity and 14 lines at the smaller, 

 where it is broken, the chambers being here filled with 

 coarsely crystalline calcite (fig. 1, a). A marble slab from 

 Sweden contains a section of an Endoceras in which a portion 

 of the body-chamber is preserved. This individual measures 



2 feet 1\ inches in length and increases very slowly in diam- 

 eter, measuring only 1 line at the apical and 1 inch at the 

 basal extremity. On the whole it would seem to belong to a 



