101 Messrs. W. K. Parker and T. R. Jones on the 



somewhat vesicular and the outline crenulate. It approaches 

 near to the typical P. crispa, and is a common variety. D'Or- 

 bigny has figured a similar form under the name of P. Listen 

 (For. Foss. Vien. pi. 6. figs. 19-22). 



8. Nautilus macellus (two varieties). Page 66, var. a. pi. 10. 

 figs, e-^; var. /8. pi. 10. figs. A-^. "Recent: Zoophytic concre- 

 tions, Mediterranean." Var. « is a sub-complanate, slightly 

 unsymmetrical Polystomella : the unequal development of the 

 two faces is an interesting feature. Var. y8 is symmetrical, not 

 quite so flat as var. «, and is lobated in its outline by a periodical 

 irregularity of growth, peculiar perhaps to the individual. Both 

 of these are thin varieties of Polystomella mspa. 



D'Orbigny has recognized the similarity of his P. Fichteliana 

 (For. Foss. Vien. p. 125, pi. 6. figs. 7, 8) to P. mncella, — a simi- 

 larity too close, in our opinion, to allow, of any distinction. 



P. macella, when plano-convex, would be equivalent to the 

 Faujasina carinata, D'Orb. (For. Foss. Vien. p. 194, pi. 21. 

 figs. 29-31) from the chalk of Maestricht. 



This variety and other flat PolystoineUce. are very common in 

 the shallow waters of the Mediterranean and the tropical seas, 

 and have been washed into the sands from the sea-weeds to 

 which they have been attached by their flattest surface. This 

 face often shows the whole coil of the spire, as in Favjasina 

 carinata, D'Orb. 



A large symmetrical umbonate variety, near to P. macella, 

 var. a, occurs in great abundance in some of the Subapennine 

 and other Tertiary sands and clays. 



Polystomella macella is more unsymmetrical than any Oper- 

 culine variety of Nummulite, but not so much so as is the rule 

 in Amphistigma vulgaris [z=A. gihba) : in the latter the aperture 

 is a large slit nearly all on the more bulging side ; whilst in 

 Polystomella macella, when most twisted in its growth, the sep- 

 tal plane and aperture are but little affected, indeed scarcely 

 more so than in the unequally gibbous Operculince. Both the 

 symmetrical and unsymmetrical Nautiloid Foraminifers delight 

 in complanate varieties ; and these are often the more irregular 

 in their growth because of their weak and starved condition. 



The peculiar twist acquired by the complanate Polystomellce is 

 equalled by that in the Australian Vertebralime, both discoidal 

 and crozier-shaped, which, although showing just the same 

 kinds of variation as they are wont to do in other parts of the 

 world (and in fossil deposits), yet have, one and all, their mouth 

 turned more or less to one side; and in the very flat discoidal 

 varieties the shells are often saddle-shai)ed. 



Polystomella, in its very small and simple varieties, as well as 

 its very large and complex forms, and also in its ol'ten prickly 



