VON BUCH ON THE CYSTIDEA. 23 



and on the side of the upper surface, exactly in this direction, is 

 found the mouth. This is well exemplified in the figure of A. am' 

 phora given in Portlock's 'Geology of Londonderry' (pi. 15. 

 fig. 4. a) ; and in A. iriacontadactylus and A. tessellatus, in the same 

 work, these relations are also indicated with the greatest clearness.. 

 Was it from inadvertence that Miller (p. 98, pi. 2) described this 

 Actinocrinite as having the mouth centrical ? The same relation be- 

 tween the basal plates and the position of the mouth upon the side 

 appears in Platycrinus, and is admirably shown by the author (see 

 Pentacrinus, tab. 6) ; and since the mouth is only centrical in those 

 cases in which the cup is based upon perfectly regular five-sided 

 plates, it is possible that Miller was not describing a true Actino- 

 crinite, but a Carpocrinite, first separated by M. Miiller (^Penta- 

 crinus, p. 32). I doubt also very much whether Melocrinus has 

 ever been seen with the mouth centrical, as it is generally on one 

 side in the direction of the smallest of the four basal plates. 



The lateral plates of Caryocrinites (costales of Miller), six in 

 number, and forming a perfect cylindrical inclosure, give to the ge- 

 neral contour considerable elegance. They are higher than they are 

 broad by about one-half, and they form more than half of the abso- 

 lute height of the cup. They rise from the intersection of the basal 

 plates, alternating therefore with these latter; and in the case of the 

 larger plates, which, as I have already mentioned, are formed of the 

 confluence of two, without a retiring angle being traceable on their 

 upper line, they rest on the longer sides of each of the large penta- 

 gonal plates formed by the soldering together of two smaller ones. 



These two inclose that one of the lateral plates which conducts 

 directly to the mouth, and form a very regular six-sided figure, 

 elongated and pointing in one direction towards the apex, and in 

 another to the base. Of the other three lateral plates, only one, 

 that namely exactly opposite this mouth-plate, is regularly hexagonal, 

 since of the remaining two the angles pointing towards the summit 

 of the cup are truncated, so that the figure is in each case changed 

 to a heptagon. 



Six scapular plates (radialia axillaria of Miiller) form the upper 

 portion of the cylindrical cup. Above the middle they are pierced 

 through, and their further development prevented by the arms which 

 rise from this part, so that only somewhat more than one-half of 

 them appears in sight. Two small plates are inserted on the trun- 

 cated angle of each of the two heptagonal plates on the side opposite 

 the mouth, and are concealed under the bases of the arms, so that 

 the rim of the cup properly consists of eight plates, six of them large, 

 with two smaller ones between them. 



This complete and perfectly symmetrical arrangement, and the 

 relation of the different parts to one another, is extremely well shown 

 in the appearance of the general form as seen Irom above (see 

 PI. III. fig. 2). Thus looking ujjon the fossil, we may see distinctly 

 how the whole of the upper part is comi)ressed into a spherical 

 triangle, from each of the angles of which rise a pair of arms, while 

 near every pair and on each side is placed another single arm. It is 



