146 CARBONIFEROUS CEPHALOPODA OF IRELAND. 



It will be noticed in the drawing that the wall of the siphuncular neck has been cut 

 through, exposing it as a short open tube. 



I think it would be a great advantage if authors were to display, whenever this 

 is possible, more than one suture-line, and thus show the distance separating the 

 chambers, as well as the relation of the sutural lines to each other. A suture-line is 

 hardly ever developed without exposing the neighbouring one, either wholly or in 

 part, and the illustrations will be more instructive when they include the latter, even 

 if imperfect. 



Afjinities. — As one of the distinguishing marks of this species, Mr. Crick 

 points out the " flattened trapezoidal form of the cross-section of its whorls." The 

 ornamentation also is so distinct and characteristic as to be in itself a sufficient 

 means of identification. The only species having any obvious resemblance to the 

 present one is l^cricyclus rotuliformis, G, C. Crick,^ but this has much less 

 conspicuous ribbing, while, on the other hand, the constrictions are much stronger 

 than those of P. trapezoidalis. 



Locality. — Clane, county of Kildare. (Mr. Crick has erroneously given St. 

 Doulagh's as the locality.) 



' 'Ann. Mag. Nat. Hist.,' ser. 7, vol. iii, p. 435, fig. 3. 



