122 BULLETIN 100, UNITED STATES NATIONAL MUSEUM 



salient and turned towards the base. The aperture is semielliptical, 

 transverse; the peristome is thick and very salient. 

 Measurements. — 



Aperture] , 



Zooecia 



Lz= 1.10 mm. 



= 0.17 mm. 

 6a = 0.25 mm. Us = 0.85 mm 



Structure. — Our specimens were living at the time of dredging and 

 provided with their ectocyst; we have therefore been able to recog- 

 nize the true structure of the zooecia. The ectocyst is thick- and 

 forms on the interior a large chitinous sack attached to the frontal 

 peristomie. The operculum remains attached to the ectocyst, but 

 it is supported on the concave border of the aperture; it is therefore 

 not arranged at the bottom of the peristomie as in the Phylactellidae. 



In consequence the 





frontal is 

 ventitious 

 ering over 

 opesium 



ad- 



only an 



frontal cov- 



the true 



of the mem- 



( ) 



Fig. 29. — Exechonella magna MacGillivray, 1895 

 A. Organisms found in cell, X85. B. Mandi- 



ble, X85. C 

 attachments. 



Operculum, X 85, without muscular 

 D, E. Two opercula, X85. 



braniporoid zooecia. 

 The pores being round 

 as in Hiantopora we sup- 

 pose they have the same 

 origin and that the 

 frontal results from the 

 union of the ramifica- 

 tions of one or several 

 oral spines; but this is 

 purely a hypothesis. 



The zooecia are very 

 deep and juxtaposed as 

 can be seen in our figure representing the zoarial section. The struc- 

 ture of the frontal is very different from that of a tremocyst (fig. 4) 

 in perfect conformity with the observations of Jullien regarding 

 Arachnopusia. 



MacGillivray, 1895, referred this species doubtfully to his genus 

 Hiantopora. We can not see any real difference between his figures 

 and our photographs. 



Biology. — This is a species of quiet waters of little depths. 

 Occurrence. — 



D. 5137. Jolo Light, Jolo; 6° 04' 25" N.; 120° 58' 30" E.; 20 



fathoms; S. Sh. 

 D. 5141. Jolo Light, Jolo; 6° 09' N.; 120° 58' E.; 29 fathoms; co. S. 

 D. 5144. Jolo Light, Jolo; 6° 05' 50" N.; 121° 02' 15" E.; 19 



fathoms; co. S. 

 Miocene of Australia (MacGillivray). 

 Plesioty 'pes. —Cat. No. 7966, U.S.N.M. 



