42 CLYPEASTER LATISSIMUS. 
tubercles with three or four still larger primaries towards the outer edges 
of the ambulacral plates. The iuterambulacral plates carry huge primary 
tubercles, three or four to each plate, arranged in UTegular concentric 
rows. These tubercles increase in size towards the central part of the 
iuterambulacral area, and then diminish again in size towards the actino- 
stoine. 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 iuterambulacral areas of the actinal side are long, 
stout, curved, slightly spathiform, and recall somewhat for Clypeastroids 
the Lovenia type of spines and of tuberculation. 
The color of these flat Laganuui-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 Lagmmm luiimmum. 
The third type, which I have figured on Plate XP. of the Revision, and 
described under the name of SMonoch/pus RureneUa, 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 snbdcpresmts and C. latissimus, and by its distant 
uniform primary and coarse intertubercular granulation. As in C. suhdc- 
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 Revi.>ion of the Echini as characteris- 
tic of the young stages of Clijpcmter suhdepresms are on Plate XIII. Figs. 
10-18; these, however, all belong to the swollen-edge type, C. Ravcncllii ; 
the other, Plate XIP. Fig. 4, is a young of C. hdmimus. An excellent 
series of the young stages of C. hdmimus 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 C. hdksimns, and the presence of ambula- 
cral furrows, show a close i-elationship between the flat Clypeastroids and the 
