116 DESCRIPTIOX OF THE HAED PARTS OF SOME 



short rounded spines passing mainly into granules similar to those cover- 

 ing the abactinal surface of the arms ; they are in addition provided with 

 one or two long flat triangular movable spines similar to those covering 

 the outer edge of the actinal side of the marginal plates, which are 

 arranged in irregular diagonal lines across the plates, varying in size, 

 generally flattened and triangular ; but we find with them, along the 

 edge of the furrows separating the plates, slender spines similar to those 

 of the grooves of the abactinal side. 



The interambulacral plates carry flat spatula-shaped spines placed at 

 right angles to the longitudinal axis of the arms ; these plates, when 

 denuded, are seen to be in contact with the marginal plates, except near 

 the actinal ring (PI. XIX. Fig. 5). Spines similar to those carried by the 

 interambulacral plates, only shorter, cover the actinal side of the jaws 

 (PL XIX. Fig. 2). 



The ambulacral plates seen from the interior of the arm occupy, with 

 the base of the interambulacral plates, the whole space between the mar- 

 ginal plates ; the median furrow formed by the junction of adjoining 

 plates is deep ; the ambulacral plates themselves are narrow, elongate, 

 spreading somewhat at their junction with the interambulacral plates, 

 leaving a wide space for the passage of the ambulacral feet. 



It is not uncommon in this genus to find the ambulacral and interam- 

 bulacral plates soldered together, either wholly or in part, so that it be- 

 comes difficult to trace the line of contact. 



In Astropecten and Luidia the interambulacral plates of the last basal 

 joint of the adjoining arms are connected together, forming a prominent 

 point at the angle of the arms ; but those plates which carry the mouth- 

 papilljB are not, as in other families of Starfishes, at a lower level than the 

 adjoining interambulacral plates. The jaws are on the same level, in direct 

 continuation of the other interambulacral plates, only somewhat more 

 prominent (see PI. XIX. Figs. 7, 8). 



Astropecten articulatus and Luidia clathrata extend from New Jersey 

 to the West Indies. Luidia clathrata is one of the most common Star- 

 fishes of the sandy coasts of North and South Carolina. 



