228 The American Naturalist. [March, 
Since the differences throughout are dependent on the dis- 
tinctive peculiarities of the larve used, it is necesssry first to 
make clear the difference in structure of the larval forms that 
we are considering. The two accompanying figures will ren- 
der a long account needless. : 
Fig. 1, A and B, represents an Echinus larva, and fig. 2, A and 
B, that of Spherechinus. The two figures oriented alike, show 
the circumference of the body and the calcareous skeleton seen 
in profile [and in front]. The differences in structure of the 
Fig. 3. 
Larva of bastard of Echinus microtuberculatus 3 and Spharechinus granularis Q - 
body, particularly in the sheltered structures, are brought in 
these figures in the position best suited to the observer. The 
arrangement is sufficiently well shown in the figures to obviate 
any further description The enucleated egg-fragments of 
Spherechinus were brought together with the sperm of Echinus. 
`The generic name will suffice, from this on, in speaking of these two species. 
PLAE S eres 
