420 Prof. M. Schultze on Polytrema miniaceum. 



paratively great transparency, were always easily referred to the 

 Rotalide type, whilst in the form which I named Acervulina no 

 such spiral nucleus had been detected; so that, without forgetting 

 that the boundaries of the families of the Polythalamia generally 

 are very artificial, and that every system cannot be satisfactory 

 in every direction, I did not hesitate to form a distinct family 

 for the sake of the preliminary revision. Nevertheless it appears 

 that the irregular increase in age occurs more frequently than 

 was previously supposed in species which showed regular spiral 

 shells, and that a spiral nucleus is to be detected in the centre 

 of many apparently quite irregular aggregations of chambers, 

 which were therefore true Acervulina. Hence it would be better, 

 with Carpenter, to adopt the irregular growth only in the generic 

 or specific diagnoses, and to give up the family Acervulinidce. 

 With this I perfectly agree, only remarking that in Acervulina 

 acinosa, the typical form on which the genus was founded by 

 nie, no spiral or other regular commencement has been detected, 

 and that, for all such forms, the genus Acervulina must still be 

 provisionally retained. In Carpenter's system, Polytrema would 

 come in the family Globigerinida, near Tinoporus, on account of 

 the spiral commencement (imperfectly seen even by that observer) 

 and of its shell-structure. Carpenteria must then be reckoned 

 among its nearest allies. 



If I say a few words in conclusion upon the systematic divi- 

 sion of the Foraminifera proposed by Carpenter, I can only give 

 my general approval of it. It is distinguished from previous 

 attempts of the same nature by its placing in the foreground, 

 for the definition of the principal groups and famiUes, certain 

 peculiarities of the shell-structure which have hitherto been either 

 employed only for the determination of genera and species, or 

 not sufficiently recognized, whilst that which has hitherto fur- 

 nished the main classificational character — the arrangement of 

 the chambers — has only a secondary importance attached to it. 

 There is no doubt that the two suborders formed by Carpenter, 

 Foraminifera imperforata and F. perforata, form sharply dif- 

 ferentiated and in themselves coherent groups. It must, how- 

 ever, be expected that, however natural the classification may be 

 in general, in detail many apparently unnatural separations may 

 occur. I instance only the dismemberment of the genus Cornu- 

 spira, one species of which has a brown, translucent, imperforate 

 shell, and the other a hyaline perforated one, although perfectly 

 similar as regards the internal cavity, the direction of the spiral, 

 the size, &c. ; so that the two species now naturally stand, with 

 different generic names, in two different suborders. 



The six families which Carpenter distinguishes are, of the 

 Imperforata — I, Gromida, with a membranous shell; 2, Milio- 



