201 



sides and a subangular margin. Aperture narrowly sagittate or 

 lanceolate with a basal truncation, deeply emai-ginated by the preceding 

 volution, outside of which emargination its height is more than twice 

 its maximum breadth. Surface smooth. Septum consisting of six 

 lobes and six saddles on each side, not counting the minute siphonal 

 saddle. Siphonal lobe about equal in height to the first lateral, and 

 composed of two main branches (one on either side of the siphuncle), 

 each of which is trilobate at is outer extremity. First lateral lobe 

 scarcely branched, but bearing three minute, irregular toothed lobules, 

 one on each side. Between the siphonal lobe and the first lateral, there 

 is an auxiliary lobe about equal in height to the second lateral. The 

 remaining lobes are simple but minutely incised and decrease gradually 

 in size and height towards the umbilical margin. Siphonal saddle 

 unknown, but obviously very small. First lateral saddle much larger 

 than any of the rest, deeply divided into two spreading branches, 

 which are variously and unsymmetrically lobed and incised. Second 

 latei-al saddle somewhat deeply lobed and cut at its outer extremity, 

 but not distinctly branched. The remaining saddles, like the corres- 

 ponding lobes, are simple but minutely toothed, and decrease regularly 

 in size towards the umbilical margin. Greatest diameter, rather more 

 than forty-nine millimetres : width of umbilicus, four and a-quarter 

 ram. : maximum thickness, eight and a half-mm. 



East point of Maud Island, in Skidegate Inlet : one imperfect 

 example. 



This shell is very nearly related to the Ammonites Eequienianus^ 

 and the A. GoupiUanus'f of d'Orbigny, especially in the character 

 of its septum. From the former, however, it differs in the minute and 

 obtuse carination of its periphery, and from the latter by its much 

 smaller umbilicus. 



The septation of S. Maudensis is not at all like that of the typical 

 species of Sphenodiscus, but the author of that genus is inclined to 

 think that its characters should be enlarged so as to include such forms 

 as A. Eequienianus. In this connection also. Dr. Fischer writes as 

 follows! : "Le type de ce genre" (Sphenodiscus) "est I'A. lobatus, 

 Tuomey. Le groupe des Clypeifonnes de d'Oi'bigny (type : A. Goupili- 

 anus d'Orbigny) correspond assez bien a la coupe g^ndrique proposee 

 par Meek." 



* Pal^ontologie Fran^aise, Terrains Cretac^s. Tome 1, p. 315. Atlas, pi. 93. 

 t " " " " p. 317. Atlas, pi. 94, figs. 1-3. 



t Manuel de Conchyliologie. Paris, 18S1. Vol. I., p. 389. 



