LAGENIDA. 29 



to a very variable amount of lateral compression, either on two, three, or four sides. Aperture 

 usually single; in the exceptional distomatous forms the two orifices are at opposite 

 ends of the shell. Shell-wall perforated by numerous very minute foramina.^ Texture, 

 hyaline. 



For our views of the relationship of Lagena, in its manifold variations, see the 'Philos. 

 Transact.,' 1865, vol. civ, p. 345, &c. The accompanying table of the distribution of 

 fossil Lagena will be of interest to geologists, who can also refer to a general list of fossil 

 and recent Zayewi®, by Prof. Reuss, in the * Sitzungsb. Akad. Wiss. Wien.,' 1862, vol. 

 xlvi, p. 317. 



In our table we have arranged the Lagence according to our scheme of the prominent 

 forms, as indicated in ' Phil. Trans.,' loc. cit., p. 348, introducing some that do not occur 

 fossil, to make the series complete; and we have introduced into the table materials from 

 the works of Reuss, Seguenza, and others, having made their nomenclature conformable 

 with ours. 



1 The keel of the compressed Lagence, and the marginal ribs of the angular varieties, are formed of 

 " the supplementary skeleton," or secondary shell, containing what has been termed " the canal-system." 

 Occasionally, as in Lagena tubifero-squamosa, P. & J. (' Phil. Trans-,' 1865, p. 420), the whole surface is 

 coated with this extra shell-growth. The circular cavities, or " lacunae," in the keel of L. ornata, shown 

 in Williamson's 'Monograph,' pi. 1, fig. 24, are really continuous with the minute pseudopodial perfo- 

 rations of the shell-wall, usually by delicate bundles of tubuli ; and they commuDicate with the exterior by 

 a coarse pseudopodial tube. 



