FORAMINLFERA I — FAMILY MTLIOLIDA. 489 



in Calcarina (Plate xvi., fig. 3) ; and it is in these that we find 

 the ' Canal-System ' attaining its greatest development. Its most 

 regular distribution, however, is seen in Polystomella and in 

 Operculina ; and an account of it will he given in the description 

 of those types. 



372. Miliolida. — Commencing, now, with the Porcellanous 

 series, we shall briefly notice some of its most important forms. Its 

 simplest type is presented by the Cornuspira (Plate xv., fig. 1), of 

 our own coasts, found attached to Sea-weeds and Zoophytes ; this 

 is a minute spiral Shell, of which the interior forms a continuous 

 tube not divided into chambers ; the latter portion of the spire is 

 often very much flattened-out, as in Peneroplis (fig. 5), [so that 

 the form of the mouth is changed from a circle to a long narrow 

 slit. Among the commonest of all Foraminifera, and abounding 

 near the shores of almost every sea, are some forms of the Milio- 

 line type, so named from the resemblance of some of their minute 

 fossilized forms (of which enormous beds of Limestone in the neigh- 

 bourhood of Paris are almost entirely composed) to Millet-seeds. The 

 peculiar mode of growth by which these are characterized will be best 

 understood by examining in the first instance the form which has 

 been designated as Spiroloculina (Plate xv., fig. 2). This Shell is 

 a spiral elongated in the direction of one of its diameters, and 

 having in each turn a contraction at either end of that diameter, 

 which partially divides each convolution into two chambers ; the 

 separation between the consecutive chambers is made more com- 

 plete by a peculiar projection from the inner side of the cavity, 

 known as the 'tongue ' or ' valve,' which may be considered as an 

 imperfect septum ; of this a characteristic example is shown in the 

 upper part of fig. 4. Now it is a very general habit in the Milio- 

 line type for the chambers of the later convolutions to extend 

 themselves over those of the earlier, so as to conceal them more or 

 less completely ; and this they very commonly do somewhat un- 

 equally, so that more of the earlier chambers are visible on one 

 side than on the other. Miliolce thus modified (fig. 3) have 

 received the names of Quinqueloculina and Triloculina according 

 to the number of chambers visible externally ; but the extreme 

 inconstancy which is found to mark such distinctions, when the 

 comparison of specimens has been sufficiently extended, entirely 

 destroys their value as differential characters. Sometimes the 

 earlier convolutions are so completely concealed by the later, that 

 only the two chambers of the last turn are visible externally ; and 

 in this type, which has been designated Biloculina, there is often 

 such an increase in the breadth of the chambers as altogether 

 changes the usual proportions of the Shell, which has almost the 

 shape of an egg when so placed that either the last or the penulti- 

 mate chamber faces the observer (Plate xv., fig. 4). It is very common 

 in Milioline shells for the external surface to present a ' pitting,' 

 more or less deep, a ridge-and-furrow arrangement (fig. 3), or a 



