FORAMINIFERA OF THE NORTH PACIFIC OCEAN. 85 



There are numerous varieties or species which by recent authors 

 have usually been placed in a single species, P. pertusus (Forskal). 

 As the various forms seem to have rather constant characters of form 

 in combination with certain characters of aperture it seems as though 

 they may really be more distinctive than has been given general 

 credit. The genus is especially common in shallow waters of the tropi- 

 cal regions, being one of the characteristic foraminifera of coral reefs. 



The young of Peneroplis pertusus have been observed by Schacko. 

 Copies of two of his figures are given (fig. 1). In this early develop- 

 ment at the time that the megalospheric young leave the parent test 

 they consist each of a globular or oval proloculum with the encircling 

 second chamber usually about a half coil in length, being very similar 

 to the early stage of the Quinqueloculine series and of Spiroloculina. 

 These two chambers have a thin shell wall of even thickness through- 

 out, the wall of the second Cornuspira-like chamber being continuous 

 with that of the proloculum and building no floor on the adjacent wall 

 of the proloculum. The apertural end of the 

 second chamber has a slightly thickened lip. 



Figure 41 shows the development seen in 

 the early chambers of the ordinary megalo- 

 spheric form, the proloculum measuring 35^ 

 in this specimen. Here, as in the young 

 specimen (fig. 1), there is a globose prolocu- 

 lum (1) followed by the elongated, coiled 

 second chamber (2) comparable to Cornuspira. 

 In Peneroplis as in the two following genera 

 (Orbiculina and Orbitolites) the first and 

 second chambers are perforated by very fine fig. 4i.-early chambers op 



Pt _ ~, J e ~~ j/u' Peneroplis pertusus, var. 



enerophs was removed from this ARIETINUS; x83 . ME ' GALO _ 



group by R humbler on this basis of perfora- spheric proloculum 35*. in 



tions, but it has since been shown by Lister DIAMETEK - 



to be equally characteristic of the early chambers of Orbiculina and 



Orbitolites. 



The third chamber (3) is more or less globular, connecting with the 

 second chamber by a narrow passage, circular in cross section. The 

 floor of this chamber is laid down on the wall of the proloculum, 

 causing an appreciable thickening. The aperture of chamber 3 is on 

 the inner border of the apertural wall and takes an oblique direction 

 as it traverses the wall of the test. This obliquity causes a thicken- 

 ing of the wall below, which is characteristic throughout the later 

 development of the test. Succeeding chambers are very similar to 

 chamber 3 in their general characters. This series of chambers 

 forms a close coiled test. In the specimen figured the first eight 

 globular chambers make up a complete coil. In succeeding coils the 

 number of chambers in a single coil is larger, as the chambers do not 

 increase in size proportionately to the increase in the size of the test. 



