326 Mr. F. Chapman on the 



XLIX. — On the Bhizopodal Genera Webbina and Vitri- 

 webbina. By Frederick Chapman, A.L.S., F.R.M.S. 



The tests of the ReticiiLate Rhizopoda usually exhibit three 

 kinds of shell-structure, and this difference forms an essential 

 element in the classification of the Foraminifera as they are 

 at present understood : — {a) The porcellanous test is opaque 

 milky white and by transmitted light of a translucent brown 

 or horn-colour, without minute foramina in the external wall. 

 {h) The arenaceous test is composed of sand-grains, sponge- 

 spicules, or other foreign material, embedded in a chitinous 

 cement, and with or without perforations in the external 

 shell-wall, (c) The hyaline or vitreous test is more or less 

 transparent, sometimes with a glassy surface, and with 

 innumerable fine tubules perforating the shell-wall or test 

 and more or less at right angles to the surfaces. 



The genus Webhina, when first brought into use, was made 

 to include those Foraminifera which consist of a series, straight 

 or curved, of hemispherical or elongate or of single chambers 

 essentially adherent to foreign bodies. The shell-structure 

 was at the time overlooked, and only indistinct ideas can be 

 gathered about many of the types from the description given 

 of the superficial appearance of the test. 



It is therefore advisable that a review of the genus should 

 be made, in order to discuss some of the chief points with 

 regard to the priority of authorship and the grounds for 

 retaining the genus Webbina. 



The generic name was given by d'Orbigny in 1839 *, to 

 include an adherent foraminifer with a rough exterior which 

 he found in sand off the island of Teneriffe. This species 

 he named Webbi7ia rugosa ; but in the diagnosis of the genus 

 no clue was given which would enable anyone to form an 

 opinion as to the nature of the test. Indeed, tliis essential 

 point of shell-structure in the description of Foraminifera was 

 generally overlooked until Carpenter, Jones, and Parker 

 conducted their elaborate researches upon it. Subsequently 

 d'Orbigny described two other specimens under the names of 

 Webbina flexuosa and W. irregularis '\ \f\\\c\i had previously 

 been figured by Cornuel X as " eggs of molluscs," and which 



* d'Orbigny, A. D., " Foraminiferes " in Barker- Webb and Berthelot'a 

 * Histoire naturelle des lies Canaries ' (Paris, 1839), vol. ii. part 2, p. 125, 

 pi. i. ligs. 16-18. 



t d'Orbigny. A. D., ' Prodrome de Pal^ontologie stratigraphique univer- 

 selle des Animaux moUusques et rayounes ' (Pai'is, 1850), vol. ii. p. Ill, 

 DOS. 782, 783. 



X Cornuel, J., " Description de nouveaux fossiles niicroscopiques du 





i 



