204 Papers from the Marine Biological Laboratory at Tortugas. 



Fig. i6. — Escharella costifera 

 n. sp. Details of front 

 wall, mucro, aviculariutn, 

 jointed spines, vestibular 

 arch (in upper figure), 

 and ovicell (in lower 

 figure). 



which rise strong, conspicuous ribs which converge regularly toward the 

 central portion of the front wall. They fade out, however, before they 

 reach it, leaving a smooth central area devoid of ribs. The orifice, which is 

 placed far forward, is rounded in front, more straight 

 on the posterior border, and the hinge denticles are 

 rather conspicuous. A few zooecia seem to show a 

 slight median denticle, but I can not be certain of 

 this. The peristome, which is very thin, rises in front 

 and on the sides into a short tube, and is beset with 

 six or eight long spines which are jointed at inter- 

 vals. Posteriorly the peristome rises into a high, 

 pointed mucro which projects forward over the ori- 

 fice. This mucro is flat and thin, with a strong rib 

 on each edge, looking as though it originated from 

 two spines fusing at the tip, leaving an open space 

 between. The development of the mucro, however, 

 shows that this is not the case. The thin area forming 

 the middle of the mucro is rounded below and pointed 

 above and looks as though it were meant to harbor 

 an avicularium, but no such structure is present. 



Avicularia are present on the zooecium, usually situated near the margin 

 on either side of the mucronate process. Occasionally only one is pres- 

 ent. The avicularium is comparatively large, the mandible long triangular, 

 projecting sidewise or a trifle backward and pointing strongly upward. 

 The ocecium is rounded in outline, prominent, imperforate, smooth on the 

 upper surface, or with fine, radiating lines. Around the margin is a strong, 

 raised rib, within which there Is a row of large pores with strong ribs running 

 upward as on the zooeclal wall. The anterior pair of spines is inclosed 

 within the ovicell. 



Two small colonies, the largest scarcely over 0.125 ii^ch across, in- 

 crusting algse, at 2 fathoms. In spite of the small size nearly every cell is 

 adult, with a complete ocecium. 



I am a little uncertain as to the generic position of this species. Es- 

 charella as amended by Levinsen (1909, p. 315) includes only forms without 

 avicularia. In spite of this difference the species seems to fit better into 

 Escharella than Into any related genus. The absence of zooeclal and ooecial 

 pores, except the marginal ones, the well-developed vestibular arch, the very 

 thin operculum, the character of the orifice and peristome, and the nature of 

 the jointed spines, seem to locate the species in Escharella. In many respects 

 it resembles E. diaphana MacGillivray, as figured by Levinsen (1. c), 

 except for the presence of the avicularia and the strong development of the 

 ribs, which are wanting In diaphana. 



