466 Fossils of the Chazy Limestone. 



of two whorls and a half the diameter of the coil is eight inches. 

 Whorls contiguous, but in the cast of the interior not in contact; 

 transverse section of the tube nearly circular: siphuncle ventral 1 

 and at the completion of second whorl, in which place only it can 

 be seen in the specimen, about three lines in diameter, aud one 

 line or a little iess from the margin. At the same point the septa, 

 as marked upon the siphuncle, are six lines distant from each other. 

 The shell is not preserved, but from the smoothness of the cast I 

 think there can be no transverse ridges, as there are in L. Jason 

 and L. undatus. 



Only a single specimen of this fine species has been collected, 

 and that is a cast in which ncne of the septa can be seen. Its 

 great size, the separation of the whorls in the cast, and the absence 

 of undulating transverse ridges, are abundantly sufficient to dis- 

 tinguish it from any other described species of the Lower Silurian 

 rocks of North America. 



Locality and Formation. — Mingan Islands; Chazy limestone. 



Collectors, — Sir W. E. Logan, J. Richardson. 



Nautilus natatok, N. s. 



Description, — Discoid planorbiform, all the whorls exposed in 

 the umbilicus. Tube slender, gradually increasing in size, so 

 that on the completion of the fifth whorl the diameter of the coil 

 is four and one fourth inches. Section oval, the dorso-ventrai 

 diameter being greater than the lateral in the proportion of about 

 8 to 6 (?) Septa at the end of fourth whorl, three in about seven 

 lines, measured on the side. Surface and siphuncle unknown. 



The specimen is imperfect ; but if it has not been compressed 

 laterally, then, as nearly as I can determine, the dorso-ventra} 

 diameter at the end of the fifth whorl is sixteen lines and the 

 lateral twelve ; at the fourth whorl five to seven ; and it would 

 appear therefore that the third must be scarcely three lines in its 

 greatest diameter. 



I have not seen the first and second whorls, but as there is an 

 empty space nine lines in diameter in the centre of the coil I 

 presume that they did once exist and occupy that space. The 

 whorls are in contact, but the outer ones are not indented by 

 those next preceding. 



Locality and Formation. — Mingan Islands ; Chazy limestone. 



Collectors. — Sir W. E. Logan, J. Richardson. 



