124 Proceedings of the Royal Irish Academy. 



limbus is drawn inwards on all sides, so that it forms a perfectly smooth 

 circular rim, the diameter of the circle being much less than that of the body. 

 This encloses a shallow basal cavity (see PI. XIY, fig. 10), whose diameter 

 is larger inside than at the mouth. The pedal disc itself, which, of course, 

 forms the inner wall of the cavity, is very thin and membranous, and the 

 mesenterial insertions show through it. In the upper part of the body the 

 wall increases in thickness, and at its thickest may be as much as "8 cm. The 

 whole upper portion is introverted, and when such a thick, solid substance is 

 squeezed together by such strong contraction, ii naturally falls into folds and 

 creases; these might be termed "capitular ridges"; but 1 am inclined to 

 think, since they are of extremely variable size, and absolutely without any 

 regular arrangement, that they arc merely contraction folds and would very 

 likely vanish if the animal were expanded. They are solid mesogloea. The 

 tentacles are in three apparent cycles at the disc margin, and the outer ones 

 pass directly into the folds of the body-wall, so that there is no definite 

 margin. The tentacles are short, Btnmpy, and of very irregular sizes; the 

 mesogloea of the lower half is very thick and still', especially on the outer 



■ and the upper part is flaccid and much more thin-walled, often with 

 a*somewhat capitate lip. (PI. XIV, fig. 11.) 



j are peculiarly arranged — the oute a are much mixed up with 



the marg ntraction-folds, and the inner ones are just free from the 



margin. The plan of arrangement, apart from minor irregularities, seems 

 to be 36 + 36 ■ 72 ■ 111 7 odd ue The oral disc is smooth and 



lirm. with a slight radial ridge i ach tentacle, which does not reach the 



mouth. Lip prominent. Two well-developed actinopharyngeal grooves. 

 Colour in spilit, white, disc and oeso] I inged brown. 



These are arranged on the plan 18p. + 18p. 

 Ti'p. = 144p., but there are actually 19 pairs in the second cycle, 

 which causes a little irregularity — apart from which the plan is almost 

 exactly i it. 36 pairs are perfi 



The last cycle mesenteries are very small, and alone bear visible gonads. 

 Small oral, but no marginal stomata, are present. A certain amount of 

 inequality in the development of the mesenteries occurs; but altogether, as 

 many pairs have the partners equal (to the naked eye al all events) as 

 unequal, and when one partner is larger than the other it is sometimes the 

 wrong partner that is larger — i.e., it violates the rule which obtains in 

 The fourth-cycle mesenteries bear male gonads, but have no 

 musculature to speak of. The rest of the mesenteries are thin. Those of 

 the third cycle are fringed along the endocoelic side with short, simple, or 

 slightly branched longitudinal-muscle processes, which do not attain the 



