46 ECHINOLAMPAS DEPRESSA. 



Echinolampas depressa Gray. 



Yucatan Bank, Lesser Antilles. 82-101 fathoms. 



PI. XVI., PI. XXIV. Figs. IS. 



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 ambulacral system, which characterize this and 

 allied species in different stages of growth, make their appearance very 

 early. In the younger stages I have figured (Revision of the Echini, PI. 

 XVI. Figs. G, 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 lateral posterior ambulacra is seventeen 

 pairs of pores shorter than the anterior zone. In a specimen measuring 

 4o 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 

 lour in the posterior ambulacra. This striking numerical difference still 

 existed in specimens measuring no less than 50 mm. in length (PI. X\ I. 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 /ones of the odd ambulacrum sometimes varying from 

 the ratio staled above as much as four to six pairs. Similar differences in 

 the length of the zones of the ambulacral petals are known in several recenl 

 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 lias separated as Palaeolampas a species of Echinolampas with 

 straight ambulacral zones, and in which the outer rows of pores are the 

 largest, and form with their rudimentary Eurrows 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. 



