ART. 14 FOSSIL AND RECENT BEYOZOA CANU AND BASSLER 65 



. r^ , ,. . J7io = 0.40-0 .45 mm. 



Measurements. — Operculum (A zooeciajU _ __ _ 



iLo = u.oU m^m. 



10.75 mm. 



„ 1 /D • nJO.60 mm. 



Operculum {B zooecia) 



„ . .[^2 = 1.00 mm. 

 Zooecia A^y „ __ 



Uz =0.75 mm. 



ry . „ 1.25-1.50 mm. 

 Zooecia B{^ „_ 



[0.75 mm. 



Structure. — Since the fine work of Harmer, 1890, and that of 

 Waters, 1913, the internal structure of this remarkable animal is now 

 very well known. We agree entirely with the masterly work of 

 Harmer, 1926. 



The ectocyst, naturally light colored, is thick and entirely covers 

 all the zooecia; it is smooth but generally dirty. The hinge of the 

 operculum is placed at the level of the orifice of the polypidian tube. 

 The trace of opesiular muscles is quite visible and revealed by two 

 concavities symmetrically disposed on the dried specimens. 



The structure of the A opercula is quite special and well known; 

 but that of the B opercula has been up to the present poorly inter- 

 preted because absolutely unexpected.. In short, it is the structure 

 of an avicularium with its rachis with two small pillars arranged in 

 a triangle. It is therefore a mandibular operculum. It fills the 

 triple function of assuring the closing of the zooecium, the entrance 

 of the hypostege and oxygenation compatible with the extreme vigor 

 of the zooecia. The hooks of the peripheral sclerite grip the mural 

 rim and assure the closing. The size of this mandibular operculum 

 is exactly that of the cryptocyst which it covers entirely and exactly 

 when the cell is open. 



The occlusur muscles of the A opercula are attached to the longi- 

 tudinal sclerites and at the level of the superior extremity of the 

 tentacular sheath; they form three vigorous bundles; we reproduce an 

 unretouched photograph. When the mandibular B operculum is 

 open all the interior of the cell thus visible is lined by a membranous 

 cryptocyst covering the entire muscular system and perforated only 

 at the level of the polypidian tube for the passage of the numerous 

 tentacles. 



Variations. — The micrometric variations are considerable. Smitt 

 had already in 1872 discovered that the size of the opercula 

 varied from 0.40 to 0.86 mm. The figures of Harmer, 1890, indicate 

 much greater variations. Our specimens from the Philippines have 

 zooecial dimensions much smaller; those from Honolulu are still 

 smaller. It is then in the Gulf of Mexico that the species devel- 

 oped best and Harmer cited the large dimensions of the specimens 

 from Jamaica. 



58613—28 5 



