106 DESCEIPTIOX OF THE HAED PARTS OF SOME 



Asterina folium. 



Aslerbia folium Lutk. 1859. Vidensk. Meddel. 



PL XIV. Figs. 7-9. 



In Asterina, as in the bulk of the pentagonal Starfishes, the great 

 lateral development of the secondary interambulacral plates introduces 

 some modifications in the structure and position of the hard parts in this 

 genus. The plates forming the actinal and abactinal floors are irregularly 

 lozenge-shaped, imbricating at the extremities of the adjoining points, 

 leaving thus a greater or less free space for the passage of the water- 

 tubes ; the plates of the two floors at the ridges of the disk become sol- 

 dered together, thus forming, as it were, a new system of plates, which in 

 some genera are regularly arranged and often furnish characteristic spe- 

 cific distinctions. At the actinal ring the interbrachial arches exist only 

 as columns rising directly from the actinal to the abactinal floors in the 

 interambulacral spaces. As in all the species of the genus, the lozenge- 

 shaped plates of the actinal and abactinal surface carry short slender 

 spines, with a more or less regular fan-shaped arrangement on the abac- 

 tinal side ; the spines are less numerous on the actinal side, some- 

 what longer on the interambulacral plates, especially near the actino- 

 stome, forming mouth-papillis of considerable prominence (PI. XIV. Figs. 7 

 and 7'). 



The simple structure of the short, pointed tei'minal tentacle at the ex- 

 tremity of the arm is well seen in this genus (PI. XIV. Figs. 8', 8); adjoin- 

 ing tentacles are, as in Asterias, long, slender, without a prominent suck- 

 ing-disk. The water-tubes are specially large in this genus (PI. XIV. 

 Fig. 9). 



This species has the same range as Linckia Guildingii. 



Asteropsis imbricata. 



Aslerupsis imbricata Grube, 1857. Wiegm. Archiv., XXIII. 



PI. XV. 



The abactinal limestone reticulation of this species consists of flat, irreg- 

 ularly star-shaped plates, from which diverge longer flat pieces, connects 

 ing the adjoining centimes of radiating plates (PI. XV. Fig. 2); the plates 

 and their connecting links are all imbricating. Towards the central part 

 of the disk the larger spaces between the rods are partially closed by 

 shorter spurs, and are further separated by disconnected plates into ellip- 



