86 WHITEAVES OX THE OBTHOCERATID.E OF 



teen millimetres iu their maximum diameter, after which the siphuncle decreases so 

 rapidly iu size that in the fourth chamber from the body chamber, the maximum diameter 

 of the segment therein contained is only five mm. Dimensions of the specimen figured 

 and described ; total length, about nine inches, or 23 cm. ; greatest thickness, 36 mm. ; 

 length of the septate portion of the shells, as measured in the median line of the section, 

 14.6 cm. ; greatest diameter of the body chamber, 35 mm. posteriorly and 29 mm. anteriorly. 



Swainpy or Beren's Island, Lake "Winnipeg, .T. B. Tyrrell, 1889 : one nearly perfect 

 cast of the interior of the shell, with the whole of the siphuncle and septa well preserved. 



The internal structure of this species is essentially similar to that of the Orlhoceras 

 docens of Barrande, which Professor Hyatt regards as an aberrant member of his genus 

 Sadoceran, but the external contour of these two shells seems to be quite different. The 

 remarks which Professor Hyatt makes upon S. docens, however, are quite as applicable to 

 the Canadian species. In reference to the former, he states that " it is a transition form, 

 but we place it in this genus because at an age when an Actinoceras would have the 

 rosettes large and perfect, this species begins to lose them, and the siphon decreases also. 

 The reduction of the siphon is a degradational senile shrinkage, and it occasions the loss 

 of the rosettes. M. Barrande views this old stage of the siphon as a return to the tubular 

 siphon, but in our opinion we cannot call this a tubular siphon. As a matter of fact it is 

 a modified nummuloidal siphon, as may be seen by comparison with others." 



GoNiocERAS Lambii. (Sp. Nov.) 



Plate XI, figs. 1, la-b. 



Shell large, its body chamber unknown, the septate portion elongated, compressed 

 conical, but increasing very slowly in size, strongly compressed on the dorsum and venter 

 and broadly expanded at the sides, which are ultimately sharply angulated ; lateral 

 diameter a little more than twice the dorso-ventral, the exact proportions being as two to 

 five ; outline of transverse section nearly lenticular, though the venter is a little flatter 

 than the dorsum. Surface markings unknown. Septa rather closely approximated, their 

 sutures averaging from ten to eleven millimetres apart on the median line of the dorsum, 

 each suture being broadly concave on the dorsuru and venter, and produced into a large, 

 obtusely pointed saddle on each of the lateral angles. Siphuncle ventral, marginal, 

 strongly inflated between the septa, bvit very small proportionately, its thickest portion 

 occupying not much more than one-seventh the maximum diameter of the tube. The 

 constrictions between the siphonal inflations are very deep, and, when viewed in longi- 

 tudinal section, appear as narrow incisions which cut obliquely backward and inward, 

 on each side, thus giving a very peculiar appearance to the siphuncle. 



Approximate dimensions of the specimen described: length rather more than ten 

 inches ; maximum diameter, at the smaller end, five inches, the corresponding diameter 

 at the larger end being six inches and a half. 



The writer desires to associate this interesting species with the name of his friend 

 and colleague, Mr. L. M. Lambe, F.G.S., who collected the only known specimen at East 

 Selkirk in 1880. It difiers from the type of the genus, the G. ancejis of Hall, in its 

 miich greater size, in the less rapid rate of tapering of its expanded sides, in the greater 



