MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 553 



incrusting colonies, or groups of more or less isolated corallites. Column wall cylindrical, elongated, on 

 retraction may almost completely cover the disk; no sphincter. Tentacles entoccelic and exoccelic, 

 incompletely tetracyclic, long and narrow, entacmseous, tubercular, with knobbed apex. Stomodteal wall 

 smooth. 



Mesenteries regularly hexamerous, incompletely tricyclic, six pairs complete, two pairs directives, 

 all filamentiferous. Septal invaginations hexamerous, entocoelic and exocoelic, incompletely tetracyclic, 

 below nearly all united centrally, forming almost distinct mesenterial loculi. 



Asexual reproduction by gemmation from the lower part of the column wall or the basal expansion. 



Example — Astrangia solitaria Lesueur. 



ASTRANGIA SOLITARIA Lesueur. 

 (Pis. V and VI. figs. 43, 44, 45, 47.) 



External characters. — The species is met with all round the Jamaica coast, mainly in 

 regions of coral growth. Polyps of various sizes occur in groups of from three or four to a dozen 

 or so, incrusting blocks of dead coral or other objects, often on their under surface. The individ- 

 uals of a group are either connected with one another by basal columnar expansions or stolons. 

 or are entirely free and separated for a greater or less distance. The corallites rise but little 

 above the surface of attachment, and the proximal region is frequently hidden by Nullipores. The 

 incrustations may continue their growth until they cover practically the whole of the external 

 skeletal surface, or even pass beyond, the column wall retreating accordingly. Where Nulli- 

 pores are absent the column wall may extend downward over the external surface of the coral- 

 lite for two or three millimeters, and continue for some distance as a basal expansion. 



The column wall is smooth, delicate, transparent, and usually circular in outline, rarely 

 oval; the diameter varies from 3 to 6 millimeters. On full expansion it exhibits longitudinal 

 ridges and furrows, and on partial retraction the wall is withdrawn a little within the calice; but 

 during full retraction it may be greatly depressed, extending centrally so as to almost completely 

 hide the tentacles and disk. The upper portions of the septa are very distinctly seen through 

 the polypal tissues, and can be readily counted and their arrangement in cycles followed. 



The tentacles are long and narrow on full expansion of the polyps, narrowing slightly from 

 their origin to the free extremity, and terminating in a white, opaque, spheroidal swelling, very 

 distinct on full or partial expansion. The tentacular walls appear unusually thin and 

 transparent, and are provided with close-set batteries of nematocysts, which stand out 

 prominently. Sometimes these are white, but are often a delicate iridescent green, more rarely 

 brown. During full extension the tentacles remain overhanging. The arrangement in cycles is 

 not readily followed, but it is easily seen that one tentacle arises over each septum, and the plan 

 can be determined from these. Six prominent septa form a first cycle, six smaller alternating 

 septa form a second cycle, while the third and fourth cycles rarely show hexamerous completion, 

 and the tentacles correspond (%. 43). The innermost tentacles arc the largest, measuring about 

 3 mm. in length. 



The disk is circular, thin-walled, and transparent, allowing the six pairs of complete 

 mesenteries to be seen through. A few minute green spots are arranged in radiating rows. 

 The mouth is very long transversely, slit-like when closed, oval when open; the lips are white 

 laterally, while the two extremities may be green. Four ridges can sometimes be made out on 

 each side of the stomodaeum; oftentimes the lips are drawn together in the middle, leaving only 

 two distinct apertures, one at each end. The mouth was triangular in one example, and seven 

 pairs of complete mesenteries could be seen through the disk, instead of the usual six. indicating 

 some structural irregularity. 



Polyps living on the under surface of blocks of coral are often colorless throughout, or 

 display only very delicate tints within restricted areas. In other cases the polyps are brightly 

 colored, brown and green predominating. The column wall may be purplish or brown, green 



additions from the septal en. Is; outer papillae resembling those of the septa, or differing in consequence of a large 

 paliform tooth being <m seme septa, s.pta unequal, net exsert, seme united, granular at the sides, denticulate, and 

 often with a paliform tooth Costse visible on the wall near the calice especially. Epitheca absent. Dissepiments 

 few and distant." (Duncan, 18S5, p. 66.) 



