NOTES ON BRITISH FORAMINIFERA. 



III.—POLYSTOMELLA CRISPA LINNE, SP. 

 Bv EDWARD HEKOX-ALLEX. l-.L.S.. F.K.M.S., and ARTHUR EARLAND. 



Next to Massilind sccans in the order of frequency 

 of occurrence in most English shore-gatherings 

 comes the beautiful species, Polysfoniella crispu. 

 If we ma\" judge by the exclamator\- opinions 

 expressed b\' casual observers at microscopical 

 soirees, this is b\' far the most exquisite of all the 

 Foraminifera, and its extreme commonness, com- 

 bined with its highh' 

 complex shell formation, 

 has attracted to it a lion's 

 share of scientific study 

 and observation. 



In domesticity, if we may 

 so call the life of these 

 Rhizopods in our obser- 

 vation tanks, it is nearly 

 as amenable to its quasi- 

 artificial conditions as 

 Massilina secaiis, and as 

 soon as the latter emerge 

 from the mud the\' will be 

 seen to be accompanied 

 b\" the more robust 

 PolystomeUae on their 

 journeys up the glass or 

 among the growing algae. 

 In this state they present 

 a magnificent appear- 

 ance: the peripheral 

 edges, and, as a rule, the 

 terminal chamber, are 

 seen to be quite trans- 

 parent, and the sarcode 

 bod}', of a deep reddish- 

 brown tint, is clearh- 

 visible inside the sheU. 

 In this species the differ- 

 ence between the deeph 

 coloured sarcode and the 

 transparent layer of pro- 

 toplasm from which the pseudopodia are pro- 

 duced, niay be very distincth' observed. The 

 pseudopodia are sparingly extruded from all the 

 pores of tht shell, producing anastomosing fila- 

 ments all round it, whilst at the terminal aper- 

 ture a principal group of long pseudopodia are 

 extended in a fan-like arrangement, sometimes to a 

 length several times the diameter of the shell. 

 These terminal pseudopodia are the first to be 

 extruded when the animal emerges from the mud. 

 and appear to have a specialised function of 

 adhesion and locomotion. When no peripheral or 

 surface pseudopodia are \-isible the animal may be 

 seen under a low power of the microscope to be 



Polystoniclla crispa JLimie 

 shell in all stages of growth 

 bottom show the shell in 



squirming about on its aperture, apparentlv seeking 

 for a suitable spot on which to anchor itself. 



The shell of Polysfoniella crispa, though al\\a\'S 

 true to a certain tvpe of structure, varies enormously 

 in appearance according to the locality and its 

 surroundings, which no doubt explains the plethora 

 of names from which it has suffered. But our British 



specimens do not present 

 any great range of varia- 

 tion, although, in any 

 large gathering, speci- 

 mens may be found 

 w hich bridge the interval 

 between it and the closely 

 allied species Polysto- 

 niclla niacella. Typically, 

 a British specimen of 

 /-". crispa is a biconvex 

 and bilaterally symme- 

 trical nautiloid shell. The 

 convex surfaces may be 

 cither flattened and com- 

 jiressed like the familiar 

 '" tabloid,"" or the convex- 

 it\" mav be pronounced 

 with the central umbo 

 standing prominently out 

 from the surface of the 

 shell. The chambers are 

 arranged in an involute 

 or embracing spiral of 

 several whorls. Each 

 indi\idual chamber is \'- 

 shaped so that it rides 

 over and embraces its 

 predecessors in the inner 

 whorls. This overlapping 

 of the chambers does not 

 quite extend to the centre 

 of the shell, and the 

 umbilical depression thus left is filled up by a deposit 

 of solid shell substance, forming an umbo, or boss, 

 which is perforated by a system of canals, which also 

 link up the chambers and through which the pro- 

 toplasm circulates. As a result of the overlapping of 

 the chambers and the secretion of the central umbo, 

 onl\- the last convolution of chambers is visible 

 externally. In appearance the shell varies from a 

 glassv transparence in living specimens, through 

 milk\- translucency to a dead white in shells where 

 the animal has been dead a long time. 



Massiliiia secans with which we dealt last month, 

 belonged to the porcellanous or imperforate group of 

 Foraminifera, which have but a single aperture and 



Specimens showing the 

 X JO. The specimens (21 at 

 edge \iew with apertnre. 



376 



