26 PEOCEEDINGS OF THE NATIONAL MUSEUM vol.76 



Measurements. — 



„ . , Zs= 1.25-1.50 mm. -r, • ^ • f A» = 0.30mm. 

 Zooecium { -, ^ ^„ . ^^ Fenstomice ' 



Iz = 0.80-1.00 mm. ^ [ ^P = 0- 25 mm. 



Structure. — The text figure represents the peristome and its orifice 

 or peristomice drawn with the camera lucida. In the distal portion 

 a large anter almost semicircular is noted. The proximal portion 

 bears a broad, convex (or almost straight) mucron, limited on the 

 sides by two concavities and laterally two orbicular indentations. 

 Two large condyles, directed into the peristomie, separate the anter 

 from the poster. The form of the operculum does not correspond at 

 all to that of the peristomice. 



In the interior of the peristomie, two small lateral, shallow cups 

 {g) are lodged in the lateral indentations. They are not covered by 

 the operculum. They are hidden by the ectocyst and they appear 

 frequently as two lucidas on the visible closure. When they are not 

 visible, the ectocyst is confused with the operculum and the closure 

 showing exteriorly has a different form, but deceiving from that 

 of the operculum. 



In the interior of the cells there is no olocyst. The visible orifice 

 which is the base of the peristomie, does not have the form of the 

 operculum. The two large condyles are visible in perspective. The 

 proximal border is rectilinear and continues to the zooecial walls in 

 order to limit two small canalicules (c) placed exactly under the 

 small cups of the peristomie. 



The operculum is black, very thick, and we have been unable to see 

 any muscular attachments. Its very special form has no analogy 

 with any other known operculum. It closes the true aperture. In 

 order that the latter correspond to it, it is necessary that it be placed 

 in the peristomie itself and limited posteriorily by the condyles, the 

 cups, and the exteriorily visible mu'cron. This very special arrange- 

 ment is, however, compatible only with a rigid operculum. In the 

 other known cheilostomes the apertura is placed at the bottom of the 

 peristomie. The mucron, visible exteriorily, is, then, not a true 

 mucron, for it does not have the protective function. It is a cal- 

 careous piece, rather variable in form, extending into the peristomie 

 up to the apertura. The tremocyst, seen by transparency, is also very 

 special and of an unusual aspect. Between the small tremopores 

 there are small clear spaces vaguely polygonal, not limited, which 

 can correspond only to the little calcified portions invisible in the 

 ordinary light. 



The ectocyst alone is a very deep brown almost black, but the cal- 

 careous walls of the zooecia are white without any trace of color. 



