148 FAMILY LITUOLIDA. 



chambers are pentangular, with five prominent carinae. And it is finally to be noticed that 

 claviform specimens occasionally present themselves, in which the primitive tvisevial arrange- 

 ment cannot be distinguished, so that nothing but their aperture indicates tlieir " valvulinc" 

 character. 



222. Afflnities. — It will be evident, from what has been already stated, that if Valvidinu 

 is to be ranked among Lituolida, it must be regarded as a very aberrant member of that 

 family ; its afiinities being at least as close to the occasionally arenaceous members of the 

 vitreous series, as they are to the typically arenaceous Lituola. In fact, it w'ould be difficult 

 to adduce a more apposite illustration of the indefiniteness that characterises the boundaries 

 of even the primary subdivisions among Foraminifera, than that which is afforded by the 

 singular combination of characters which this genus presents, and by the approximation to 

 that combination exhibited by certain aberrant modifications of such genera as Textularia and 

 Bulimina, whose proper place is unquestionably among the vitreous-shelled Foraminifera. 

 Points of resemblance are not wanting, however, between Valvulina and certain porcellanous 

 types : thus in the tendency of the spiral growth to give place to rectilinear elongation, even 

 at a very early stage, we are reminded of the articuline elongation of Verfehralhia ; while the 

 partial occlusion of the large aperture by a valvular flap (of which the small genus 

 Sphceroidina and some varieties of Hotalia present the only examples in the vitreous series) 

 is a remarkable link of affinity to Miliola, which is strengthened by the parallelism w-e have 

 seen to be exhibited by the most developed forms attained by this valve in the two genera 

 respectively. 



223. Geofjrapliical Dislribulion. — The typical form of Vnlviilina is less common at the 

 present time than it seems to have been at earlier periods ; and the genus is now 

 represented rather by its trochoid, clavuline, and other modifications. The former present 

 themselves in all seas, being of smaller size and less frequency in the northern than in the 

 southern ; and it is along the Australian shores, and in shell-deposits among Coral-reefs, that 

 we meet with the highest development of the trochoid and of the large-mouthed forms, whilst 

 the clavuline occur not merely in the Australian but in the Indian and Atlantic Oceans, in the 

 Red Sea, and in the Mediterranean. 



224. Gcolofjical BiMribution. — The earliest specimens of this type at present known 

 occur in the Cretaceous period ; but it is in the Eocene Tertiaries of the Paris basin that it 

 seems to have first attained a high development, both as to number and variety of forms. It 

 appears- to have continued as a common inhabitant of the littoral zone through the successive 

 periods of the Tertiaiy epoch ; and the assemblage of forms presented by the Grignon 

 deposits is almost exactly paralleled by that which may be collected at the present time near 

 the coast of Australia. 



