1894- CEPHALOPOD BEGINNINGS. 431 



also suggests that it was, during life, filled with some material that 

 exerted pressure on its walls ; the material would naturally be the 

 generative glands. 



The conical apex of the shell is not septate, but is entirely filled 

 by the so-called sipho, which, before it passes through the first- 

 formed septum, is greatly swollen so as to occupy all the space in 

 the cone behind this septum, except a small wedge-shaped space next 

 to the septum. This at least is what I gather from the following 

 sentence, which I quote because I do not quite understand it. " The 

 first septum seems not to conform to the contracted surface of the 

 cone, which has a much greater obliquity, and there thus appears to 

 be an irregular wedge-shaped cavity between these two surfaces, but 

 there is no evidence whatsoever that the conical end of the sipho 

 was in any way involved in this cavity except at its upper surface." 

 This conical end of the siphuncular tube was covered by a very thin 

 coating of shell, " a mere film." It has, however, been preserved to 

 us, and preserved more constantly than any other part of the shell, 

 owing to the fact that it became lined during the life of the animal 

 by a secondary deposit of carbonate of line (Fig. 3, a). This deposit 

 is very similar in structure and appearance to the well-known guard or 

 rostrum of the belemnite ; but, since it is inside and not outside the 

 phragmacone, it cannot possibly be homologous therewith. It 

 may better be compared to the plug of secondary calcite that 

 repaired the ends of many individuals of Orthoceras, which were 

 broken during life, or to the deposit that lines the siphuncular 

 passage of Adimcevas (Fig. 6). Considerable stress is laid by 

 Clarke on the fact that a break occurred during the deposition of 

 this secondary calcite, so that it is divided into at least two portions 

 " the line between which is represented only by a faint streak or 

 difference in the texture." And this he regards as " indisputable 

 evidence that the sipho enclosed or was composed of siphonal sheaths, 

 as in Piloceras, Vaginoceras, and Endocems." (See Fig. 5, I). This, 

 nevertheless, I for one propose to dispute a little later on. 



Before proceeding, however, with further criticism, it seems ad- 

 visable to point out the very close resemblance that exists between 

 these specimens now described by Clarke and specimens described 

 nine years ago by Holm (10), which were found in beds of almost 

 identical age in Oeland, Esthonia, and Prussia. A rough sketch 

 (Fig. 4) made from some of Holm's figures by my friend A. H. Foord 

 (9) is here reproduced, as it shows better than anything else could do 

 the extraordinary likeness that obtains between the Etidoceras heleviniti- 

 fovme of Holm and the Nanno aulcma of Clarke. In both we see the 

 relatively close septa, penetrated by a wide siphuncular passage on 

 the extreme margin (Fig. 4, c) ; the constriction of this passage by 

 the septa, which bend downwards as septal necks and curve upwards 

 towards the shell aperture on the side of the siphuncle ; the swelling 

 of the passage so as to fill almost, but not quite all the apex of the 



