﻿104 W. J. SoUas—The Genus WehUna. 



not tuberciilate. — Formation, Cambridge Greensand. — Locality, Cam- 

 bridgesbire. 



2. W. tiihercuJata, mihi, Figs. 4 to 9. — Surface of test ornamented by 

 a number of tubercles irregularly dispersed, generally hemispherical 

 and depressed, resembling the rivet-heads on an iron girder, but some- 

 times conical and transversely truncated, average diameter 0-00115'^, 

 height O'OOOS'''. In some specimens the tubercles appear to be larger 

 and more numerous than in others. A section of this species, includ- 

 ing some instructive longitudinal sections of its tubercles, is repre- 

 sented in Fig. 7. 



From an examination of these it will be seen that each of the 

 bosses of the exterior is but the superficial portion of a structure 

 which enters deeply into the test. This structure has the form of a 

 double cone, such as would be produced by two cones fusing to- 

 gether by a common base, the outer and shorter one rising into a 

 tubercle on the exterior, the longer and inner one reaching inwards, 

 nearly, but not quite to the interior face of the test. The longitudi- 

 nal axis of this skittle-shaped column or double cone is occupied by 

 a canal about 0-0009 of an inch in diameter, simple and cylindrical 

 in the exterior cone, but in the interior one constricted and dilated 

 alternately either in an annular or spiral fashion, as shown by the 

 waved outline of its margins in section. 



Exteriorly the surface of the test is slightly raised to form a 

 mound about the projecting cone, and internally the substance of the 

 test immediately imbedding the penetrating cone is traversed by 

 tubuli as elsewhere, which, however, stop short of the cone itself. 



Formation, Cambridge Greensand. Locality, Cambridgeshire. 



BemarJcs. — As the contents of the Cambridge Greensand bed have 

 been subjected to very considerable attrition, it is just barely pos- 

 sible that W. Icevis is simply W. tuberculata, with its outer tubercles 

 worn off. The smooth, beautifully finished appearance of the former 

 species does not lend any suj^port to this conjecture however, nor do 

 careful sections made across its shell exhibit the interior ends of the 

 tubercular columns, which of course would remain after the exterior 

 parts had been worn away. The conclusiveness of this latter critical 

 test is, however, somewhat diminished by the difficulty of obtaining 

 complete and perfect slices of such minute objects as these forms. I 

 have not been able myself to obtain a section of more than an arc of 

 the wall of W. Icevis, and the completeness of the section of W. tuher- 

 culata shown in Fig. 7 is entirely due to the accident of its having 

 been preserved imbedded in hard coprolite, which afforded it a firm 

 suppoi't on all sides in the process of grinding down. 



Alliances. — The minuteness of the tubulation would appear to ally 

 these forms to the Eotaline series of Foraminifera, and the irregular 

 method of their growth to Planorhulina, to the coarse perforations 

 and projecting points of which genus the perforated columns of 

 Webbina tiibercvlata present indeed a certain sort of resemblance ; in 

 external form there is an absolute identity of character between W. 

 Icevis and Trochammina irregularis. 



Summary. — That the tubulated Webbina, simulating the truly arena- 

 ceous Trochammina, should be found in tolerable abundance in the 



