lO SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I28 



VV., 350 to 400 fathoms ; hypotypes of figures 7 and 9 (U.S.N.M. No. 

 P 2i93a,b) and unfigured hypotypes (U.S.N.M. No. P 2194) from 

 Challenger station 23, off Sombrero Island, West Indies, 450 fathoms ; 

 and hypotype of figure 10 (U.S.N.M. No. P 2188) and unfigured 

 hypotypes (U.S.N.M. No. P 2194) from Challenger station 24, Cule- 

 bra Island, north of St. Thomas, West Indies, 390 fathoms. 



Discussion. — In the early stages (fig. 6) P. luculentum is typically 

 textularian in that the aperture is at the base of the final chamber, 

 but in mature specimens (figs. 8, 9) the aperture migrates into the 

 face of the terminal chamber, becoming terminal, and a rare individual 

 or "freak" develops a bigenerine stage as shown in figure 7. 



A count was made of the apertural characters of our specimens of 

 this species. Of 283 specimens examined, 249 had a biserial test and 

 a terminal aperture (88 percent) ; 25 had a biserial test and textu- 

 larian aperture (8.8 percent), but these were largely juvenile forms; 

 5 had terminal uniserial chambers and terminal aperture (1.8 percent) ; 

 and 4 specimens showed a multiple terminal aperture (1.4 percent). 



Brady (1884, p. 365) concluded that this migratory feature of the 

 aperture was of minor importance and included his species in Textu- 

 laria. He stated that this distinctive apertural character led to the 

 proposal of a distinct genus Proroporus; however, the latter is a 

 calcareous form and species referred to it probably belong to Bolivina 

 and Loxostomum. Goes ( 1896, p. 24) has called attention to the fact 

 that Textidaria saulcyana d'Orbigny, 1839, may be a dwarfed form 

 of this species and if so should take preference over this specific name. 

 However, until types of d'Orbigny's species are examined, the writers 

 prefer to keep the two forms separate inasmuch as d'Orbigny's draw- 

 ings seem somewhat generalized. 



Planctostoma, new genus, differs from Textularia Defrance in 

 having an aperture in the later stages terminal on the last chamber 

 rather than at the base of the last chamber. It is differentiated from 

 Bigenerina in lacking the uniserial stage of that genus. The rare 

 specimen here illustrated (fig. 7) with the bigenerine stage is regarded 

 as a "freak." From Siphotextiilaria this genus is differentiated in 

 lacking the quadrangular outline of that genus and also in having a 

 rounded aperture instead of a slitlike aperture on the terminal face 

 with a projecting rim. Planctostoma as presently known is represented 

 by the species luculentum and saulcyana, both from the Caribbean 

 region. Specimens figured by Lalicker and McCulloch (1940, pi. 16, 

 fig. 22a-d) as Textularia saulcyana d'Orbigny from the Pacific are not 

 this species and should not be confused with T. saulcyana. 



