NOTES ON RETICULARIAN RHIZOPODA. 55 



form shell/ the authors prefer to regard the trochoid, often 

 adherent variety {Tr. squamata, J. and P.), as the type of 

 the genus. The tenuity and fine texture of the arenaceouii 

 investment rather than the mere general contour has very 

 properly been accepted as the essential distinction, and fresh 

 forms possessing this character have one by one been added 

 to the genus until it has come to include a series having a 

 very wide range of morphological variation. Not only have 

 we trochoid and Rotaliform, but nautiloid, Milioline, Spiril- 

 line and, as we shall presently see, Lageniform and Nodosarian 

 modifications of the type. In addition to these there are 

 certain simple adherent organisms, described by d'Orbigny 

 under the name Wehhina^ whose natural affinity is with the 

 same group ; in point of fact the term Trochammina , with 

 these repeated additions, has come to comprehend an assem- 

 blage of forms having the dimensions of a Family rather than 

 a genus. The series is now altogether too bulky and diverse 

 to be zoologically convenient, and it is necessary to consider 

 whether it may not be subdivided with advantage. Prof, 

 von Reuss makes a distinct genus of the Spirilline non- 

 septate forms, to which he gives the name Ammodiscus, and 

 this term has been generally adopted by German authors. 

 If we accept Wehhma to distinguish the simpler adherent 

 varieties and Ammodiscus for the free, non-septate forms, and 

 limit the application of Trochammina to the well differen- 

 tiated septate modifications of the type, to which it was first 

 applied, there only remain the Nodosaria-\\ke species to be 

 provided for, and for these the term Hormosina^ would be a 

 suitable, generic or subgeneric appellation. I venture, there- 

 foi*e, to propose the following arrangement of the group. 



It must be borne in mind, however, that the allusions which 

 have been made to the minute structure of the test apply 

 only to specimens existing under normal conditions, i.e. in 

 sea water of ordinary salinity. I have elsewhere shown* 

 that if the proportion of mineral constituents is from any 

 cause reduced, as in river estuaries and brackish pools, the 

 arenaceous investment of the Trochammina becomes less 

 calcareous, and specimens may sometimes be found under 

 such circumstances, which are scarcely altered by treatment 

 with acids. Such individuals are still sandy and preserve to 



1 Nautilus inflatus, Montagu, 1808, ' Test. Brit. Suppl.' p. 81, pi. 18, 

 ^^.^.—Rotalina inflata, Williamson, 1868, 'Rec. For. Gt. Br.,' p. 50, 

 pi. 4, fig. 93, 94. 



" ' Foram. Canaries,' p. 125. 



^ From opfioQ, a necklace. 



* 'Ann. and Mag. Nat. Hist.,' ser. 4, vol. vi, p. 38, 51, &c., pi. 11 

 fig. 5, a — c. 



