46 ECHINOLAMPAS DEPRESSA. 
Echinolampas depressa Gray. 
Yucatan Bank, Lesser Antilles. 82-101 fathoms. 
PI XVI., Fl. XXIV. Fiffs. 1-5. 
The Blake dredged in the Caribbean a number of specimens of this 
species. They are interesting as showing that the important modifications 
in the petaloid region of the ambulacra! system, which characterize this and 
allied species in different stages of growth, make their appearance very 
early. In the younger stages I have figured (Eevision of the Echini, PI. 
XVI. Figs. 6, 7, 17, 18, 19, 21), the early development of the petaloid am- 
bulacra and the unequal growth of the different poriferous zones of the 
ambulacra are quite striking. In a specimen measuring 37 mm. in longi- 
tudinal diameter, the left petaloid poriferous zone of the odd anterior ambu- 
lacrum is four pairs of pores shorter than the right. The anterior zone of 
the anterior ambulacra is fourteen pairs of pores shorter than the posterior 
zone, and the posterior zone of the hiteral posterior ambulacra is seventeen 
pairs of pores shorter than the anterior zone. In a specimen measuring 
45 mm. the difference in the number of pairs of pores between the same 
poriferous zones was greater by three in the anterior ambulacra, and less by 
four in the posterior ambulacra. This striking numerical difference still 
existed in specimens measuring no less than 50 mm. in length (PI. XVI. Figs. 
1, 3, G), but is by no means constant, the difference between the number of 
pairs of pores in the anterior and posterior zones of the lateral ambulacra or 
in the right and left zones of the odd ambulacrum sometimes vaiying from 
the ratio stated above as much as four to six pairs. Similar dilTerences in 
the length of the zones of the ambulacral petals are known in several recent 
and fossil species of the genus. This naturally suggests the propriety of 
subdividing the genus Echinolampas. This has been attempted in part 
by Bell, who has separated as Palteolampas a species of Echinolampas with 
straight ambulacral zones, and in which the outer rows of pores are the 
largest, and form with their rudimentary furrows embryonic petals. De 
Loriol has shown the difficulty of taking this character alone as basis for a 
generic division ; but it would be convenient were we to take the living types 
alone, and subdivide the genus Echinolampas proper into sections, one con- 
taining the ovoid forms with distinctly petaloid ambulacra of equal length, 
