272 



each bearing two rows of zocecia, with their basal surfaces towards each 

 other. 



Stat. 163 A, Challenger (British Museum). 



Euthyris obtecta Hincks. 

 Annals Nat. Hist., Ser. 5, Vol. X, 1882, pag. 96, PI. 16, figs. 32—37. 

 Harmer, Quart. Journ. Micr. Science, n. s. Vol. 46, 1903, pag. 277, PL 15, 



figs. 13—14. 

 (PI. XV, fig. 2 a— 2 f). 



The zooecia are slightlj^ calcified, arched, from a narrow proximal end ex- 

 panding distally, with a distal end obliquely ascending towards the frontal cover- 

 ing membrane. When seen from the frontal surface they seem to be cylindrically 

 oval, while from the basal surface of the colony they are of a lyre-shaped out- 

 line. The strongly projecting covering membrane is directly connected with 

 the separate zooecia only in the periphery of the aperture of the latter, and be- 

 sides only in contact with them through rod-shaped or ridge-like processes 

 from their surface. The aperture is provided with two well-developed, rounded 

 hinge-teeth. Its anter is semi-circular and rather high and its poster about half 

 as high- In the latter we may more or less distinctly distinguish between two 

 proximally converging lateral portions and a central portion. The accessor}' part 

 of the operculum has a well-chitinized margin, on either side of which there is 

 a small, tubercle-shaped process corresponding to a small, rounded indentation 

 on the pi'oximal side of each hinge-tooth. In the somewhat neck-shaped part of 

 the zocecium proximally to the aperture we find a circle of 8 — 10 superficial, 

 uniporous rosette-plates and a larger number (15 — 20) are scattered over the 

 entire basal surface. There are further nujjierous, uniporous rosette-plates in the 

 basal part of the distal wall, and a zigzag row of about 8 such plates in the dis- 

 tal half of each lateral wall. 



The connection between the projecting covering membrane and the cryptocyst 

 is brought about, as far as the frontal and basal surfaces are concerned, by 

 means of a number of thin, compressed, almost filiform calcareous prolongations, 

 which join the covering membrane with a T-shaped terminal part. These struc- 

 tures appear on the frontal surface only on the two outer series of marginal zooecia 

 on either side, and on the series next to the outermost one they only appear in a 

 number of 2 — 3 a little pi-oximally to the aperture and near the outer margin. 

 In the distal half of the marginal zooecia they are present in a larger number 

 of about 4—7. On the basal surface they are found in all zooecia in a number 

 of 4—12. On the middle row of zooecia we find the distal half of each zocecium 



