﻿58 MR. F. W. 0. RYMER JONES ON SOME J A VAN BEEP-SEA LAGEN^E 



irre- 



and tlie base. The shell has a very short internal tube ; and a few blunt bosses are 

 gularly disposed over the external walls. 



Some forms are provided with an additional pair of spines, ■^\ hich occupy the extreme 

 base, and the knob-like protuberances are absent from the shell-walls. 



In the lenticular form depicted in fig. 35 the spikes arc still present; but the outlyinf' 

 pair are removed a little higher up the sides, the intervening space betAveen them beinc 

 occupied by a thin film of transparent shell-substance, which passes round the base. The 

 internal tube is also deficient. Prof. Williamson has figured a young form from Shet- 

 land (Monogr. p. 10, pi. i. fig. 21 a) the base of which is furnished with a row of about 

 nine sharp, feeble spikes. 



In a more elongated and pyriform example represented in fig. 36 the periphery is 



encompassed by a narrow marginal border, which projects at the centre of the base into 



a two-pronged spike, one of which (perhaps originally both) bears at its apex a small 

 round knob. 



Lagena vrLGARis, Williamson, var. clypeato-marginata, Nov. (Fig. 37.) 



Shell subovate, somewhat shield-like and compressed, very broad at the base, and 

 rapidly narrowing above, where it is produced into a tolerably long neck-tube, the walls 

 of which are very solid throughout, especially at the apex, thus giving more the appear- 

 ance of a straight canal than of a neck properly so called, which also passes into the 

 interior in a very short straight internal tube. Prom the middle of the base" project two 



spikes (one only being seen from each lateral aspect) , which are sometimes very short 

 and blunted. 



The periphery is encompassed by a wide marginal " outwork " formed of three layers 

 of shell-substance, which are strengthened and united for a considerable distance by a 

 transparent rim along their outer border, originating at the anterior end, and, passing 

 under the basal spike, overlap the base of the flask below the insertion of the spme. The 

 two outer layers are tolerably regular in outline, and pass round the base in a gentle 

 curve. The middle one, however, projects beyond these, and is extremely translucent 

 and n-regularly serrated. The greater part, especiaUy the anterior portion of this com- 

 pound margin, is not so glassy, being more opaque, and having a somewhat striated 

 appearance The walls are smooth, transparent, and very finely foraminated. 



ine sHeU appears as though it were formed by the union of two shield-like valves-an 

 .^TT ""^"^ '' *^' "^^^^ noticeable from their each terminating in the long spine. 

 _ ii ^'T'^ ^'"^'^'^ P^'^^^^ ^^^^^ i^^te^d of over each spike ; but this, though 



Ugen^ TtaeAKis, Williamson, var. pelasnm^argmata, Nov. (Figs. 38, 39.) 



witl. xni^r ;L£"\r" " '"^ ''°"'P--«d, its external waJIs densely coverj 



b anuies. The periphery of the shell is encompassed by a wide marg"^ 



\ 



1 



