ART. 14 FOSSIL AND EECENT BEYOZOA CANTJ AND BASSLER 



55 



semielliptical, with a convex proximal border and two rather deep 

 lateral opesiular indentations; it is surrounded by a very little sali- 

 ent cushion. The ovicell is small and endozooecial. The onycho- 

 cellarium is as large as the adjacent zooecia, elliptical or fusiform; 

 its opesium is oval, the point below; the mandible is large, ornamented 

 with two membraneous wings forming an oval ensemble attached to 

 a rachis triangular proxunaliy and setiform at its extremity. 



^ . f7iO = 0.25mm. 

 -Opesmm 



Zooecia 



Measurements.' '^^j^^LKXLLL ^ ^ „_ / -^t. • i \ 



to = 0.25 mm. (with opesiules). 



is = 0.70-0.80 mm. 



Z2 = 0.40-0.50 mm. 



Variations. — Not a zooecium resembles its neighbor nor does a 

 single onychocellarium resemble another; polymorphism is consid- 

 erable. The frontal 

 bears three facettes — a 

 median facette formed 

 by the cryptocyst and 

 two lateral facettes 

 formed by the enlarge- 

 ment of the mural rim — 

 but they are not regular. 

 The orientation of the 

 zooecia is indecisive, a 

 phenomenon rather rare 

 in the encrusting bryo- 

 zoa and caused here by 

 the presence of certain 

 zooecia which engender 

 two or three equal zoo- 

 ecia and by the position 

 of many onychocellaria 

 intercalated sporadic- 

 ally between two ad- 

 jacent longitudinal 

 series. 



Structure. — The ecto- 

 cyst is thick. The oper- 

 cular valve is completely surrounded by a kind of peristome formed 

 by the small cushion v/hich surrounds the opesium; it is itseK bor- 

 dered distally and laterally by a little thickened sclerite but of a deeper 

 color. The dimensions are rather constant and shghtly transverse, 

 namely, length of opercular valve 0.16 mm.; width, 0.16 to 0.18 mm. 

 The aperture exactly closed by the valve is bordered by a large scler- 

 ite, placed on the internal side of the cushion and attached to the two 

 extremities of the opercular sclerite. On the external side of the 



B C 



Fig. 7.— Velumella ameeicana new species. A. Portion of 



THE ECTOCYST, X 85, COVERING THE OPESIUM, SHOWING THE 

 APERTURAL STRUCTURE. B. DRAWING, X 85. C. MANDIBLE 

 OF THE ONYCHOCELLARIUM WITH THE ELEVATOR AND OCCLUSOE 



MUSCLES, X 85 



