852 Dr. E. von Dcaday on a 



Morphology and Chemical Composition of the Shell. 



The form of the shell, as already remarked, may be com- 

 pared to that of the shell of a flat Helix , the whorls of which 

 are coiled from left to right. In this respect our Polythala- 

 mian agrees with the genus Botalia^ belonging to the faniily 

 GlobigerinfB, Carp. ; but while in the Botalice, as Max 

 Schultze remarks, specimens coiled to right and left are 

 equally abundant*, I found the direction of the whorls in 

 all specimens constantly from left to right. Consequently 

 Entzia belongs to that series of forms in which the chambers, 

 according to Max Schultze, are arranged in a spiral — that is, 

 the group Helicostegia, d'Orb. 



The apical surface is always convex, that is to say, the 

 first chamber is placed liigher and the following ones gradu- 

 ally descend, so that the last chamber comes to be the lowest. 

 Tlie natural consequence of this arrangement is that the basal 

 surface of the shell is somewhat concave, and therefore that 

 a dorsal and a ventral surface may be distinguished, upon the 

 former of wliich the whorls and chambers Jiiay all be clearly 

 distinguished, while on the latter only the chambers of the 

 last whorl are visible. The dorsal and ventral surfaces 

 show themselves most distinctly when the shell is looked at 

 from the edge ; and in this respect our Polythalamian resem- 

 bles the Eotalinee and Bosalina ornata, d'Orb. 



In fully developed s))ecimens the chambers always form 

 two complete whorls, and in each whorl there are eight 

 chambers, according to which 1 am probably justified in 

 setting the number of chambers of the developed specimens 

 at sixteen. And this I may do the more positively because 

 among the numerous specimens which 1 have passed in review 

 I have not met with a single one with more, but very many 

 with fewer, than sixteen chambers. Thus I have found speci- 

 mens M-ith 6, 10, 12, 13, and 14 chambers. The latter 

 scarcely admit of any other inteipretation than that they are 

 to be regarded as young individuals in various stages of deve- 

 lopment, Avhich would have subsequently become developed 

 into individuals with sixteen chambers. The correctness 

 of this notion seems to be decisively proved by the fact that 

 the corresponding chambers of the individuals with 6, 10, 12, 

 13, 14, and 16 chambers are of almost exactly the same form 

 and size. 



The outer margin of the shell and of both Avhorls, as in the 

 Botalinee, is slightly waved and sinuous, in consequence of the 

 convexity of the individual chambers; in other respects the 

 surface is quite smooth. 



* 'Ueber den Organismus der Polythalamien,' p. 69. 



