130 DR A. MILNES MARSHALL ON THE 



The stalk of the first specimen (PL XXI. fig. 18) is cylindrical, with an 

 average diameter of 21 mm. It presents a slight terminal dilatation at its 

 lower end, and is marked on both dorsal and ventral surfaces by shallow median 

 longitudinal grooves. The stalk has a length of 15 mm., and is continuous 

 above with the rachis, the transition from one to the other being marked by 

 the first appearance of the leaves. 



The lower part of the rachis is flattened dorso-ventrally, and has a transverse 

 diameter of 2*6 mm. It is marked by upward continuations of the median 

 dorsal and ventral grooves of the stalk. 



As we pass from the region with immature leaves to the part of the rachis 

 bearing fully developed polyps, the rachis gradually becomes reduced in width, 

 and in the upper part, where the polyps have attained their full size, it becomes 

 cylindrical, with a diameter in the first specimen of - 5 mm., forming in fact 

 a very thin fleshy investment to the stem. 



Tlie stem is cylindrical at its upper end, with a diameter of 4 mm.; it 

 remains of nearly uniform size throughout the whole length of the rachis, but 

 tapers gradually as it passes down the stalk. It is of considerable brittleness, 

 especially in its upper part. 



The polyps commence in the lower part of the rachis as small transverse 

 ridges placed very close together, the first 6 mm. of the rachis having 20 of 

 these ridges on each side. Passing upwards, the ridges become more pro- 

 minent, wider, and situated further apart, each being divided at its free edge 

 into three polyps. 



Of the three polyps of a ridge, the dorsal one is from the start the smallest 

 of the three, and the ventral one the largest; and these proportions are retained 

 throughout. 



As the polyps get larger, the groups move further and further apart, until the 

 interval between successive groups on the same side of the rachis is about 

 3 mm., which appears to be the limiting distance. 



The ridges on the lower part of the rachis are so placed that while the 

 dorsal polyps of the ridges of the two sides are almost in contact with one 

 another in the mid- dorsal line, the ventral polyps are separated from one 

 another by nearly the whole width of the ventral surface of the rachis, an 

 arrangement which persists also in the fully formed polyps (fig. 2). 



The groups of polyps are from the first placed, not opposite one another, but 

 alternately, as shown in figs. 1 and 2, the right hand group being a little in 

 advance of the left one. 



The polyps of each fully developed group are almost completely independent 



of one another, their bases alone being united together, so that it is hardly 



possible to speak of distinct leaves. The inclusion of the species in the genus 



Virguldria is fully justified, however, by the general mode of development of 



