GENUS NODOSARINA. 161 



lie differentiated it being presented by mere varieties of the British D. legumen. And he does 

 not seem more inclined to retain the genus Bobulina, which is founded on varietal forms 

 of Crutellaria. Thus we see that, in so far as he had the opportunity of making a sufficiently 

 extensive comparison of these protean forms, he was led to conclusions of the same kind as 

 those here advocated on the basis of a more comprehensive study of them. In no group is 

 the artificiality of M. D'Orbigny's method of classification more apparent; and there is none in 

 which the results of painstaking research have been more fruitful in elucidating the close 

 natural affinities of organisms, whose diversity of form at first sight appears to require their 

 wide separation from each other. — It will be convenient in the first instance to describe the 

 typically straight and the typically sjnral forms of this genus ; and then to notice the inter- 

 mediate links by which the two are connected, and the chief varietal modifications which 

 diverge from them in diff'erent directions. 



245. NoDOSARiA : External Characters. — The elongated shell of this organism consists 

 of a series of segments joined end to end in a straight line ; these segments sometimes 

 exhibit a progressive increase, so that the entire shell has somewhat of a conical form ; whilst 

 in other cases each segment has the same diameter as the preceding, so that the general 

 form of the shell is cylindrical ; and it occasionally happens that the middle segment is 

 larger than those which precede and follow it, or even that the primary segment may be the 

 largest, and that the size of the succeeding segments progressively diminishes. The pri- 

 mordial segment is often furnished with a more or less prolonged macro. The segments are 

 marked externall}'^ by more or less definite constrictions, which are transverse to the axis of 

 growth ; sometimes these constrictions are simple bands, the successive segments being in 

 contact with each other over the whole of their septal planes (ex, figs. 3G, 38) ; whilst in 

 other instances the segments are nearly globular in form and are connected together by 

 narrow necks, so that the entire series looks like a string of beads (Plate XII, fig. 2). 

 That such differences have no specific value, is fully proved by the fact that they occasionally 

 present themselves in the several segmental divisions of one and the same individual. The 

 septal plane is circular, and the aperture occupies its centre ; that of the last segment is 

 sometimes situated at the extremity of a long neck resembling that of a Lagena, and is sur- 

 rounded by a row of triangular denticles (ex, figs. 36, 37) ; but the margin is usually rather 

 inverted than everted, and such a broad, smooth lip as is common in Lat/ena and in 

 Vvigerina is rare in this type. Although the surface is sometimes smooth, yet it is more 

 frequently rendered uneven by longitudinal flutings or ribbings (ex, figs. 36 — 38), or by the 

 projection of numerous spines from every part of the exterior (Plate XII, fig. 2). The 

 number and degree of these inequalities are extremely subject to variation ; sometimes the 

 costse or spines do not show themselves equally on all parts of the shell, and they are gene- 

 rally stronger on old than on young individuals. — The large Nodosarice of the Sub-Apennine 

 tertiaries sometimes attain a length of more than an inch ; but tlic recent forms are far 

 smaller, few of them much exceeding 1-1 0th of an inch in length. 



246. Internal Structure. — When the shell of Nndomria is examined by sections taken 

 in various directions, it is found that the greater part of it is penetrated by tubuH of extreme 

 minuteness, wliich pass directly fi'om the interior of the chambers to the external surface ; these 

 tubuli, however, do not extend into thecosta) or thespine.s, which are everywhere composed of 



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