42 CLYPEASTER LATISSIMUS. 



tubercles with three or four still larger primaries towards the outer edges 

 of the ambulacral plates. The interambulacral plates carry huge primary 

 tubercles, three or four to each plate, arranged in irregular concentric 

 rows. These tubercles increase in size towards the central part of the 

 interambulacral area, and then diminish again in size towards the actino- 

 stome. The intertubercular space is closely packed by a minute miliary 

 granulation. The miliary granules of the actinal and abactinal surface carry 

 short, sharp, straight miliary spines; these are somewhat larger, and curved 

 on the edges of the furrows and over the petaloid ambulacra. The large 

 primary spines of the interambulacral areas of the actinal side are long, 

 stout, curved, slightly spathiform, and recall somewhat for Clypeastroids 

 the Lovenia type of spines and of tuberculatum. 



The color of these flat Laganum-like specimens is bright yellowish green 

 when alive ; the large spines are of a lighter yellow color. This species is 

 undoubtedly the one Hupe referred to Laganum Missimum. 



The third type, which I have figured on Plate XI C . of the Revision, and 

 described under the name of Stolonoclypus Ravenellii, is characterized by 

 the thick-swollen edge and the high central part of the test, by the large 

 open petals with the distant pairs of pores, succeeding pairs being about 

 twice as far apart as in C. subdepressus and ('. laUssimus, and by its distant 

 uniform primary and coarse intertubercular granulation. As in C. subde- 

 pressus, the granulation covers the abactinal surface uniformly. On the 

 actinal side it is coarser, more distant, the tuberculation becoming smaller 

 as it passes into the ambulacral areas, leaving the greater part of the am- 

 bulacral plates merely covered by a fine miliary granulation. 



The figures I have given in the Revision of the Echini as characteris- 

 tic of the young stages of Clypeaster subdepressus are on Plate XIII. Figs. 

 10-18; these, however, all belong to the swollen-edge type, 0. Ravenellii ; 

 the other, Plate XIF. Fig. 4, is a young of C. latissimus. An excellent 

 series of the young stages of C. latissimus shows that in these very flat 

 Clypeastroids the needle-like or separate' lamellar pillars forming the inner 

 partitions become united together at their extremity, either simply at the 

 base or along the whole height of the pillar, so as to form more or less 

 irregular concentric and dendritic partitions or isolated pillars arranged in 

 concentric rows. 



The structure of the partitions in ('. latissimus, and the presence of ambula- 

 cral furrows, show a close relationship between the flat Clypeastroids and the 



