GENUS PENEIIOPLIS. 87 



which will augment with the length of the septal plane, whilst through the multiple pores of the 

 last septal plane the sarcode-body can extend itself into pscudopodia. These may coalesce 

 at their bases to form a continuous segment, on which a ne\A' chamber will be moulded when 

 the growth of the body requires such an extension of the shell* 



126. Variefk's. — The most frequent departure from the typical form presented by 

 Fenewjjlis is that represented in fig. 12 ; in which we see that, instead of opening out and 

 encroaching on the previous whorls, the spire becomes disengaged, and prolongs itself in a 

 straight hne, its successive chambers exhibiting little or no increase in size. Between this 

 and the typical form every intermediate gradation presents itself; and it is curious that 

 even here a transverse extension sometimes takes place, quite suddenly, by a doubling 

 backwards of the last three or four chambers along the inner margin of the straight portion. 

 In these elongated varieties of Fencroplis we find the spire less compressed, so that the septal 

 plane is wider in proportion to its length (fig. 12, a); and this condition, which is also 

 frequently encountered in specimens that have not thus extended themselves, is almost 

 always coincident with a duplication in the series of pores in the septal plane. Now, it is not 

 a little remarkable that this is almost uniformly the case with specimens furnished by 

 particular localities, whilst those obtained from others not very remote exhibit almost as 

 uniformly the extremest elongation and narrowing of the septal plane, with only a smgle 

 row of apertures ; and hence it might not unreasonably be maintained that this difference 

 should be accounted of specific value. In reply to this, however, there is not only the 

 analogy of Orbiculina and OrbitoUtes, in which (as we shall hereafter see) an indefinite 

 multiplication in the rows of inarginal pores may take place during the growth of tlie 

 individual, but also the fact that in Penerojjlis the two forms cannot be distinguished at an 

 early age, either by the shape of the shell or by the disposition of the pores, which are often 

 arranged neither in a single nor in a double row, but on a sort of mixture of both plans, as 

 shown in figs. 6, a, 10 ; whilst among the more advanced examples of each type it is not at all 



* A figure is given by Prof. Elirenberg (xxxis, taf. ii, fig. 1), professing to represent the 

 decalcified body oi a. PeneropUs obtained alive from the Red Sea, which corresponds with the description 

 above given in every important particular save this, that the successive segments are connected along 

 the inner margin of the convolutions by a baud much broader and thicker than the threads which 

 pass between other parts of the segments ; so that this baud would seem to establish a principal con- 

 nexion, to which the other threads might be considered as secondary. Now after a very careful 

 examination both of the septal planes of numerous specimens and of sections taken in the direction of 

 Fig. XIX, I feel myself justiQed in tlie positive assertion that no such principal aperture exists at the 

 inner margin of the septum, as would be required to give passage to such a band as is figured by 

 Prof. Ehrenberg. Consequently I can only account for this feature in his delineation of the animal 

 (the idea of a difference in the conformation of the shell being negatived by the precise correspondence 

 between his figures of it and my own, as well as by my familiarity with the Red Sea type of 

 PeneropUs), by supposing that, like some of his other figures, it rather represents his idea of the 

 structure of the animal than what he actually saw iu its body, this principal baud being apparently 

 regarded by him as an intestinal canal by which he supposed all the segments to be connected 

 together. 



