80 THE FORAMINIFERA 



custom, we give under protest names to the new trigonal forms in 

 the beUef that by this redudio ad absitrdum the older names may 

 be swept away, and the forms in future spoken of as merely 

 '^ trigonal growths " of each particular species. 



As if to emphasise our difficulty, specimens have turned up of 

 L. Orbignyana and L. dathrata, possessing four keels (PI. IV., 

 Figs. 2 and 3). These require distinctive appeUations, so we 

 must name them Z. quad rlgo no- Orbignyana and L. quadrigono- 

 daiJu'ata respectively. 



Probably, the trigonous form which appears to be common to 

 all the flat Lagence is the analogue of the double form of the 

 round ones. In this case, it seems likely that two individuals, or 

 embryos, have coalesced before forming the shell, and by their 

 adhesion together one of their four sides is suppressed, the exter- 

 nal surface being reduced by contact so as to develop but three 

 more or less perfect sides. In all cases, as in the double forms, 

 the additional portion is developed upon the same type as the 

 rest, thus supporting the validity of their specific unity. 



We have bilocular forms of Lagena, of the following species, 

 viz. : — sulcata, davata, IVilIiamsoni, costata, squamosa, caudata, 

 and Lyellii. Of these, Z. sulcata and Z. clavata are attached late- 

 rally, with a common neck ; Z. caudata, longitudinally, with diva- 

 ricating apertures ; Z. Willianisoni, L. costata, and Z. squamosa, 

 anterio posteriorly ; and finally, Z. Lyellii is similar to the last, 

 except that the posterior chamber embraces a portion of the ante- 

 rior one in a Nodosarine manner. 



In the trigonous forms, the third rib sometimes stops short of 

 the base of the shell, and consequently does not join the others at 

 that part. It seems never to fail in reaching the apex. 



Lagena lucida (PL II., Fig. 7). — Oval in section, with linear 

 fissurine mouth, in which are punctures through the linear dia- 

 phragm. This has a translucent surface, with a broad, semi- 

 opaque horseshoe band on each side, caused by minute tubules in 

 the shell-substance, usually broadly ovate, cuneate; an elliptical 

 form, with an acute base, is named Z, acuta, by Brady. 



The trigonal form of Z. lucida has been known as oblonga. 

 Lagena trigono-oblonga {lucida), PL III., Fig. 4. 



Lagena l.^vigata (PL II., Fig. 6). — This is half as large 

 again as Z. lucida usually is, has not the peculiar marking, is 

 rounder in section, longer and more uniform in shape, ovate 

 lanceolate obtuse, the fissurine aperture is as in Z. lucida. This 

 form is commoner in 50 fathoms, and seems to represent Z. lucida 

 at that depth, as Z. costata similarly supplants Z. Williamsoni, 

 which it also exceeds about as much in size. 



