771 



ul. 



interrupted. One of the specimens has the wall of the conch adhering to the 

 -iphi'iial uall along this surface. The same fact is shown in Holm's figure of 

 Hn,i \nnno) Mtmnitit'ormt. It will be observed from the figure that the 



cvlinilrir.il portion of the sipho has about one-fifth of the diameter of the entire 

 -lu'll at its widest point. 



Upon examination of the interior structure of these siphones they are found to 

 be completely solid in the apical portion for usually about one-half the length of the 



-ptal cone, but in some instances this solidification extends for the entire length 

 of the cone and into the cylindrical part of the tube. The cavity of the sipho above 

 this filling is a narrowly conical chamber whose walls gradually become thinner 

 from the apex upward, their upper edge appearing to be rounded off and finished. 



The substance of the siphonal cone and walls is invariably very compact, 

 radially crystalline calcite, indicating, inasmuch as all the specimens have been 

 found in calcareous shales and clayey limestones, a simple modification of the original 

 organic deposit; the internal cavity is filled with the mud of the sediment. Cross- 

 sections of the cone in both directions show evidence of a dark, concentric, presum- 

 ably organic discoloration, which may represent an internal sheath, but this seems 

 the less probable as this layer affords no surface of easy displacement of the parts, 

 nor does the radial structure of the calcite appear to be at all interrupted by it. I 

 should be disposed, rather, to regard it as a trace of an organic remnant of the 

 fleshy sipho, left in its anterior progress with the growth of the shell. 



The sections have afforded no evidence of a tube connecting the apices of these 

 sheaths, the endosiphon of Hyatt. The addition of the septate portion of the shell, 

 as shown in a single specimen which appears to be nearly complete, gives the species 

 a fusiform and symmetrical appearance, broadest below the aperture, the sipho 

 seeming to extend nearly the entire length of the shell. The septa are 

 gently and regularly concave, slightly inclined toward the sipho, and there were 

 apparently about twelve in the length of the shell as preserved. The first septum 

 seems not to conform to the contracted surface of the cone which has a much greater 

 obliquity, and thus the first air-chamber appears to be an irregular, wedged-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 proxi- 

 mal surface. The apical cone was unquestionably external except so far as 

 ensheathed by a mere coating or film of the shell-tube. 



The dimensions of these specimens are as follows: A nearly complete sipho 

 has a length of 36 mm.; its greatest width is at 19 mm. from the apex and measures 

 10 mm. in major, and 8.5 mm. in minor axis; its a pert u ml diameter* are Sand '' mm. 



