PENTACRINOID LARVAE 203 



The column consists of 28 columnals and a terminal plate. The first six columnals 

 are of roughly equal lengths, short and discoidal. The remainder are somewhat barrel- 

 shaped; each is encircled by a narrow median girdle and, with the exception of a small 

 number following the discoidal columnals and a small number at the distal end, is 

 slightly longer than broad. The articular faces of the longer columnals are broadly oval, 

 the long axes of those of the two ends of one columnal being at right-angles to one 

 another. The long axes of the opposing faces of two contiguous columns coincide. For 

 these reasons the alternate articulations of a part of the column appear, from some 

 angles, to be of different kinds. The terminal plate is thick and rounded. 



The base of the basal cup is not wider than the proximal columnals. Its height is 

 equal to that of the oral cup ; it is considerably less than its distal diameter. The lateral 

 edges of the oral plates are more strongly bent outwards, especially proximally where a 

 furrow lies between those of adjacent plates, than in the pre-brachial stage. 



A small rounded radial plate is present in each of the angles between the basals and 

 the orals. To the left of and a little below one of them which is smaller than the others 

 is a slightly smaller plate, the radianal. In this radius the suture between the basals and 

 that between the orals are not in line with one another as in other radii : the former is 

 slightly to the left of the latter with the anal plate lying directly in hne with it ; the radial 

 is in line with the suture between the orals. 



3. Length of crown i-o mm. (Fig. 21 c); length of column 5 mm. 



The column consists of 25 segments and a terminal plate and is similar to, though 

 shorter than, that of the previous stage. Most of the columnals are encircled by a strong 

 median girdle. The terminal plate is small, round and simple. 



The basal cup is about two-thirds as long as its distal diameter. Its base is not wider 

 than the proximal columnals ; its sides are only slightly convex. The oral cup is a little 

 longer than the basal. The radials are very much bigger than in the previous stage; the 

 corners of the basals are cut away to receive them. The right posterior radial is strongly 

 asymmetrical being undeveloped on the left side where the much smaller radianal plate 

 lies. The right distal angle of the posterior basal is strongly cut away to accommodate 

 the radianal plate. Each of the radials except the right posterior bears a small costal, and 

 a smaller axillary ; they lie in the furrow between the strongly turned out lateral edges 

 of the oral plates but are massive enough to project beyond the edges of them in profile. 

 The right posterior radial bears no ossicles. 



The suture between the posterior and the right posterior basals and that between the 

 corresponding orals are only a little out of line with one another. 



4. Length of crown i-o mm. ; length of column 4-6 mm. 



The column is of 27 segments and a terminal plate and is similar to that of the 

 previous stage. The first seven columnals are short and discoidal ; the second is slightly 

 longer and wider than the others which are of equal size. The terminal plate is thick and 



circular. 



The proximal edges of the basal plates are slightly rounded. The base of the basal 

 cup is wider than the proximal columnals. It is shorter than its distal diameter and 



