158 FAMILY LAGENIDA. 



to' the conclusion that it cannot be maintained as of even specific value, on account of the 

 variability of the degree of the introversion. It may be so complete that none of the neck 

 appears externally, the shell having a nearly globular form, and the tube reaching almost to 

 the posterior extremity of its cavity. On the other hand it may be so partial that the greater 

 portion of the neck is extruded ; and between these two extremes there are numerous inter- 

 mediate gradations (ex, figs. 16a, 22, 25 — 28). In the entosolenian as in the ectosolenian 

 forms, there is sometimes a tube at each extremity ; and occasionally there is a second inter- 

 nal tube attached to the side of the principal. — The entosolenian form presents a yet greater 

 variety of external ornamentation than the ectosolenian ; for not only do we find the surface 

 marked with longitudinal costae, but these costae may be connected by transverse bars, so as 

 to cover the shell with a regular division into quadrangular areolae ; and this may give place 

 to a hexagonal areolation, which may be of various degrees of fineness (ex, figs. 17, 18, 29 

 — 32). In certain cases the globular or ovate form gives place to one more or less compressed ; 

 and each margin is then usually elevated into a carina or keel. In a curidus variety 

 noticed by Prof. Williamson (ex, p. 11, fig. 24) the mai'ginal carina contains numerous small 

 detached cavities like microscopic water-bottles with straight necks, each of which opens by a 

 minute aperture at the outer edge of the carina. In these compressed marginate forms the 

 tubuli of the shell usually open for the most part in a broad band along the marginal ridge, 

 although occasionally thc}'^ are scattered sparsely over the whole surface. In these forms, 

 moreover, the introverted apertural tube does not project axially into the cavity of the shell ; 

 but follows the curvature ofj and is in contact with, one of its lateral walls, in some cases 

 coalescing with it so that the tube is only complete on one side, the other side being formed 

 by the shell-wall ; and sometimes its direction is more or less sinuous. — The length of the 

 Entosolenian variety is usually between l-70th and 1-lGOth of an inch, corresponding closely 

 with that of the typical Larjena when allowance is made for the introversion of the neck. 



239. 3Ionsfrositi('s. — Besides the departures from the typical form which have been 

 already noticed, an abnormalitj^ occasional!)' presents itself in this genus, which is of much 

 interest, as showing how gradationally it passes into the polythalamous forms of the same 

 family. Specimens are of no unfrequent occurrence, in which a superadded segment is 

 attached obliquely to the side of the original one ; but now and then it happens that the 

 additional segment is formed in the axis of the original one, so as to imitate the mode of 

 growth of Nodomria. Sometimes the nature of such specimens may be decided by their surface 

 ornamentation ; their lageniform character being marked by a reticulation never presented in 

 the Nodosarine group. But if the markings consist of a simple costation or furrowing, such 

 as is common to both types, the decision may be difficult ; as is the case with certain specimens 

 found in the Tertiary sands of Bordeaux, rich in Laf/ena and small NodosaricB ; which 

 specimens, being two-celled and furrowed, may be considered either as young individuals 

 of Nodosaria hnyicauda, or as monstrosities of Lar/cna sulcata (Parker). 



240. Jffinilics. — In the general simplicity of its structure, Lac/ena is related to Orbuliiia ; 

 differing from that type, however, in the possession of a single definite aperture and of the 

 prolonged neck on which it is situated, as well as in the more elaborate structure and orna- 

 mentation of its shell-substance. On the other hand, Larjena is so intimately related to certain 



