41 



from the Queen Charlotte Islands is then comparative!}^ small. In the 

 onter whorl of A. Laperousianus there are nine or ten obliqne grooves or 

 constrictions, in that of A. Seranonis there are only four. 



Septution unknown. 



Inscribed to the menior}- of the gallant Commander of the yis/ro/a^-', 

 who visited these islands in 1^86. 



A. Laperousianus probabl}- belongs to Dr. Waagen's sub-genus Peri- 

 sphinctes, the 3'oung shells of which are said to be marked by periodical 

 constrictions. Other writers regai'd these marks of arrests of growth as 

 one of the distinguishing features of the Ligati, and the species is 

 evidently one of the connecting links between that group and the 

 Planulati. Its full characters have yet to be ascertained. 



Group 6. Ligati, D'Orhigny. 

 Ammonites Timotheanus, Maj^or. 



Plate III., %ires 2, '2a. 



A. Timothninus, Mayor. Pictet et Roux. "MoUusques ties Gres Verts," page 39. 

 Plate II., fig. 6, and Plate III., figs. 1, 2. Stoliczka, "Cretaceous Cephalopoda of 

 Southern India." Series 3, parts 6-9, pages 146, 147, Plate LXXIII., ligures 3 to 6. 



Shell composed of rather closely involute, nearl}^ square whorls, 

 which become rounded with age; umbilicus about one-third the entire 

 diameter; surflice almost smooth, but marked by distant, periodic 

 constrictions.. 



As far as can be ascertained from the rather imperfect specimens, 

 about one-fourth of the innei- whorls is exposed. In two of these, 

 whose diameter is less than as many inches, the periphery of the outer 

 whorl is flatten prl, the sides are obliquely compressed, and the umbilical 

 faces are straight and steep. The squareness of the whorls is very 

 marked at this stage of growth, but the outer angles are more rounded 

 than the inner ones. Their aperture is subquadrangulai-, and wider 

 than high, even if the basal emargination (which is squarish and 

 moderately deep) is not taken into account. The proportions of the 

 umbilical opening are best seen in these half grown shells. In an 

 individual whose greatest diameter is fourteen lines, the width of the 

 umbilicus is five lines; its margin is bluntly angular. A larger but 

 less perfect specimen, which measures nearly three inches and a-half 

 across, has nearly circular whorls, but they are still a little com- 

 pressed at the sides. Its aperture is ovately orbicular, but widest 



