Dixon — On Sagartia vennsta and Sagartia nivea. 113 



Description. 

 Form 



Base — Adherent, slightly exceeding the column. 



Column —Cylindrical, sometimes pillar-like ; in height gene- 

 rally exceeding the diameter ; smooth, or slightly corrugated ; 

 studded on the upper half with suckers, which form more or less 

 distinct warts ; and on the upper third perforated hy cinclides ; 

 marked with numerous longitudinal lines corresponding to the 

 insertions of the mesenteries, which shine through the body-wall. 

 Substance fleshy. 



Bisk — Sometimes flat, but in large specimens generally con- 

 cave and expanded, so as to exceed and overhang the column ; 

 margin more or less undulate ; outline either oval or circular ; 

 radii inconspicuous, forty-eight in number, of which twenty-four 

 run from the mouth to the feet of the tentacles of the first row, 

 and the remaining twenty-four, which alternate with those just 

 mentioned, are subdivided by the insertion of secondary and ter- 

 tiary radii, which run to the feet of the tentacles in the second and 

 third rows, respectively, but do not reach the mouth. 



Tentacles — In number, 192 ; set in four rows, of which the first 

 and second contain each twenty-four, the third forty-eight, and 

 the fourth, which is marginal, ninety-six. This would appear to 

 be the usual arrangement, though slight deviations are not infre- 

 quent. Those of the first row, when extended, are about as long 

 as the diameter of the disk, and are generally turned upwards and 

 outwards : the tentacles in the other rows diminish gradually, and 

 are bent back further ; those in the outer row are frequently ex- 

 tended horizontally to the disk : they are small, and sometimes 

 contracted to the condition of mere papillae, so as to form a fringe 

 to the margin. 



Mouth — Generally swollen and gaping, frequently thrown 

 into lobes, sometimes raised on a cone, furnished with either 

 one or two oesophageal grooves ; lip tumid, and marked with 

 ridges, which terminate the radii ; a pair of oesophageal tubercles 

 mark the juncture of the oesophageal groove with its corresponding 

 radius ; specimens with two grooves having, of course, two such 

 pairs of tubercles ; throat ridged ; acontia emitted freely and 

 copiously through the cinclides and the mouth. 



K 2 



