A. EARLAND ON OKBICULINA ADUNCA. 89 



light amber brown when examined by transmitted light or in 

 transparent sections. Owing to the absence of foramina through- 

 out the family to which I have already alluded, the only means of 

 communication with its surroundings which the animal possesses 

 is through the oral aperture at the extremity of the latest formed 

 portion of the shell. Through this opening the sarcode body of 

 the foram exudes in its search for nutriment, and I shall try and 

 demonstrate that the nature and position of the aperture, which 

 differ in the several genera, exercise a considerable influence in 

 the growth of the shell. Orbiculina, in common with Peneroplis 

 and a few other Miliolidse, frequently presents a pitted appear- 

 ance under the microscope, but it can be easily shown by means 

 of sections that these depressions are merely superficial markings, 

 and are not continuous through the entire thickness of the shell 

 w^all. 



The family of the Peneroplidinse consists of four genera only, 

 and as these four are a very complete series displaying a gradually 

 increasing complexity of structure, I propose in a few words to 

 describe the generic features of the less complex forms before 

 touching Orbiculina. The first genus and the simplest in struc- 

 ture is Cornuspira, founded by Schultze in 1854. It contains 

 those Imperforate Foraminifera in which the sarcode body is con- 

 tained is a simple porcellanous tube without internal divisions or 

 septa, and coiled upon itself in one plane. The only aperture for 

 the emission of the sarcode is the open end of the tube, which is 

 sometimes slightly constricted. Now this, as you will see, is a 

 very simple and elementary form of shell, and as such might be 

 expected to have a considerable range both in time and distribu- 

 tion. Such is actually the case, for it ranges from the Lias to 

 the present day, having now a world-wide distribution from the 

 shore line to nearly 2000 fathoms. 



The next genus, Peneroplis, shows a marked advance in 

 complexity of structure. Starting, as usual, with a primordial 

 chamber, it continues its growth by means of a succession of 

 segments which are arranged in a more or less spiral manner in 

 one plane. The interior cavities of these segments are entii-e — 

 that is to say, they are not subdivided into chamberlets by internal 

 partitions. The aperture for the emission of the sarcode consists 

 of a more or less regular and sieve -like series of openings on the 

 outer face of the last formed segment. The above are the only 



