20 



C. D. Walcott — Paleozoic Pteropods. 



not yet been noticed in any American species of the genus, 

 although observed in some species of the genera Conularia and 

 Matthevia. It is the presence of a transverse diaphragm in the 

 tube towards the apex. This appears to have caused the shell 



Matthevia. Description of Figures. 



1, Side view of a small but characteristic form of the shell, la, End view of 

 same, lb, Outline, from the apex. 



2, End view of one of the more circular shells enlarged to show the surface. 

 The shell is broken away near the summit, and shows the cast of one of the inner 

 chambers. 



3, Operculum associated, in the same hand specimen of rock, with M. variabilis. 



4, Longitudinal section of conical shell. A, B, inner chambers. C, chamber of 

 habitation. S, thick shell between the inner chambers, s', s', position of the 

 septa separating the chamber of habitation and the inner chambers. 4a, cross- 

 section taken a little above the septa. 



5, Enlargement of the surface of a septum. 



6, Cast of the chamber of habitation aud the inner chamber within the septa 

 (5, s') of the most common form of the shell. 



