244 Dr. G. C. Wallich on the Difflugian Bhisopods. 



front and side views of the extreme variety, D. cassis*, in which 

 it will be seen that the characters of the marsupiform series attain 

 their maximum development. The well-marked inversion of the 

 lip and the extreme excentricity at once denote this form as being 

 the furthest removed from that in which the lip is everted, namely 

 D. lageniformis (2 c). 



Lastly, fig. 1 y represents D. Arcella as a subspecies springing 

 directly from the embryonic form. In it we perceive the reappear- 

 ance of the inverted lip, whereby it is allied to the marsupiform 

 series, and the vertical depression which, in some of the plain 

 globular forms, renders it so difficult to determine whether the 

 specimen presenting it is an aberrant D. Arcella or D. globularis ; 

 whilst at fig. 1 2 is given a member of the allied Actinophryari 

 subfamily, the Emjlyphidce, related to Diffitigia Arcella both in 

 virtue of its purely chitinoid test and the nature of the surface- 

 marking in one of the species {E. margaritacea). Difflugia Arcella 

 hence constitutes the connecting-link between the two subfamilies. 



Plate XVI. 



Fig. 1. Side view of a young specimen of the subspecies D. globularis-, 



1 a, front view, showing aperture. 

 Fig. 2. Side view of somewhat advanced state of the same; 2a, front 



view. 

 lig. 3. Side view of the early stage of the oblique or marsupiform series; 



3 a, front view. 

 Figs. 4 & 4 «. Same views of a still more advanced stage of the same. 

 Fig. 5. Side view of horned variety of D. marsupiformis j 5 a, front view. 

 Fig. 6. D. cassis, side view ; 6 a, front view. 

 Fig. 7. D. mitriformis, showing presence of the usual sandy granules on 



the posterior four-fifths of the test, whereas the anterior fifth is 



composed of chitinoid cylinders. (This form was figured by me, 



but very imperfectly, in the 'Annals' for June 1863, PI. 10. fig. 12.) 

 Fig. 8. Two-horned specimen o{ D. mitriformis. 

 Fig. 9. D. pyriformis, from Greenland, showing how completely the test 



is made up of frustules and valves of diatoms {Eunotia and Ta- 



bellaria). 

 Fig. 10. Common form of D. pyriformis, showing moderately large sandy 



granules. 

 Fig.W. D. acuminata, made up of tabular mineral particles. 

 Figs. 12, 12 fl, [2 b, 13 a. Small specimens of mitriform and acuminate se- 

 ries. In fig. 12 a crystalline body has been added to the test. 

 Figs. 13 & 14. Oblong variety, showing the apertural band. 

 Fig. 15. D. lageniformis, showing incipient eversion of lip. 

 Fig. 16. D. lageniformis, mature specimen, showing hyaline everted margin 



of the lip. 

 Fig. 17. D. globularis, typical form, but made up of large sandy particles. 

 Fig. 18. -D. tuberculata, mineral matter consisting, in a great measure, of 



minute diatoms. The test of this form is mulberry-shaped. 

 Fig. 19. D. corona, front view, showing crenulate margin of aperture; a 



six-horned variety. 

 Fig. 20. A somewhat smaller four-horned variety ; side view. 

 Fig. 21. D. globularis, from Greenland, chiefly made up of minute diatoms. 

 Fig. 22. Plain variety of D. aculeata, showing the transition from the 



plain globular to the oblique form, and the incipient inversion of 



the margin of the aperture. 



* Cassis, a helmet. 



