OF GAL WAY. 27 



On the other hand, the number of these is very small, compared 

 to the vast numbers that are fairly true and persistent in most of 

 the well-recognised types, so that, considering that the term species 

 itself is arbitrary, it is open to question, whether forms which have 

 kept true to their distinctive features through geological epochs 

 are not as well entitled to the designation of " species " as any 

 apparently better-marked and differentiated groups of animals. In 

 this case, Lagena would rank as a genus, and well-established 

 forms as species. 



ECTOSOLENIAN LAGENA. 



Lagena sulcata. — Flask-shaped, meridional ribs, some of 

 which are continued down the neck, straight or twisted spirally 

 around it. Unconnected ribs are often interposed to prevent 

 crowding at the poles ; the sulci between the ribs are deep and 

 broad. We figure a curvilinear variety, as Lagena curviliiieata^ of 

 which the typical form is derived from Lagena striata. In sulcata 

 and some others the curve of the body sweeps into the neck. 



Lagena semistriata. — This is like a decanter of moulded 

 glass, with a few short moulded ribs protecting the broadest part 

 near its base. This gives an obcuneate contour to the shell, 

 which is sometimes sub-globose, with the short ribs occurring 

 alternately nearer or further from the base. The tube and lower 

 half of the shell is usually smooth. 



Lagena striata. — Shape oval or oblong ; the ribs are much 

 finer and more closely set than in sulcata., and the shell is more 

 delicate in outline and structure. The shore-form is usually long 

 and narrow ; the length about four times its breadth. In this 

 variety the striae are continued from the posterior end, and are 

 either straight or twisted on the short tube. In from 40 to 70 

 fathoms of water, the form is broadly oval ; length about twice the 

 breadth or less, with a crown of a double circle of tubercles at the 

 posterior end, the striae terminating in this crown, and the tube 

 being reticulated by the crossing of longitudinal by transverse 

 spiral striae. The slightly tapering tube is nearly the length of the 

 oval of the shell. In both varieties the tube is inserted rather 

 abruptly, the oval of the body, not as in sulcata, becoming pyri- 

 form by sloping to the tube. 



Lagena Lyellii is equally delicately formed. The shell is 

 broadly ovate, with a broad, short, tapering neck, having a castel- 



