Thurammina papillata Brady : a Study in Va7'iation. 535 



In 1888 Agassiz refers (Eef. 17) to the occurrence of T. papil- 

 lata in his " Three Cruises of the ' Blake,' " and reproduces one of 

 Brady's figures. 



In 1889 Sherborn and Chapman record (Eef. 18) T. papillata 

 for the first time from Tertiary beds, from the London Clay of 

 Piccadilly, and figure a spherical type with few irregular papillse. 



In the same year Dreyer, in his Monograph on the organisms 

 with " pylom," or papillate orifices (Eef. 19), refers to Brady's 

 abnormal figure of T. pa'pillata (Eef. 12, pi. xxxvi, fig. 12) (in 

 which an internal shell connected by tubes with the outer sphere 

 is figured), as a noteworthy exception to the rule of construction 

 upon which he founds the theory of concentric skeleton systems 

 set forth in the work. He describes Brady's specimen as " the 

 effort of a thalamosphere in the direction of concentric develop- 

 ment, but no more, as may be sufficiently concluded from its 

 incomplete development and its quite isolated occurrence." 



In 1890 Haeusler published an important Monograph upon 

 the zone oi Ammonites transversarius of the Swiss Jurassic (Eef. 21). 

 In dealing with Thurammina he states that in the Upper Jurassic 

 T. "papillata is uncommonly variable, and even goes to the extent 

 of stating that it is " incontestably the most variable of all animal 

 species ; it is in fact difficult to convince oneself that the countless 

 number of forms can all belong to a single species. The recent 

 T. papillata is characteristically much more constant." As we 

 shall see later on, Haeusler's conclusion must have been based 

 largely on the few published figures of recent Thurammina^, and 

 he can have had no experience of the endless variations observable 

 in recent material such as has passed through our hands. It will 

 be remembered that in his 1883 paper (Eef. 8) he observed that 

 " the recent Thurammina is very variable." It becomes clear that 

 his observations upon a more extended range of material had led 

 him to alter his views. Dealing with Thuramminopsis he defines the 

 difference between this and Thurammina as : (1) Thurammina 

 always possesses a single hollow chamber; (2) Thuramminopsis 

 possesses an internal rectangularl}^ intersecting system of broad 

 cylindrical tubes wliich correspond with funnel-shaped depressions 

 upon the outer surface of the shell ; but he admits the existence of 

 typical individuals devoid of tubes, and also of the surface depres- 

 sions, which may be taken as pass;ige forms between the two 

 genera. He indicates a further difference between the two genera, 

 in the surface texture of the shell, the particles in Thuram- 

 mina being built in as a mosaic, so that the resultant surface is 

 quite smooth ; whilst in Thuramminopsis the particles are disposed 

 more irregularly in the cement, so tliat the surface has a rougher 

 appearance. But, as we shall see from the " Goldseeker " speci- 

 mens, this distinction has no constant value, many unquestionable 

 specimens of T. papillata having a roughly irregular surface ; and 



