962 BECOUD OF CURRENT RESEARCHES RELATINQ TO 



of the ventral region of tLe arms are covered with small flattened 

 sjjines placed close together and intermixed with larger spines, so as 

 to recall to mind the covering of the ventral surface of the LuidicB ; 

 the adambnlacral plates even bear, as in the latter, a comb of com- 

 pressed spines, the direction of which is perpendicular to that of the 

 ambulacral groove and the innermost of which is recurved like a 

 sabre, as in the Astropectinid^. The ambulacral tentacles are quad- 

 riserial at the base of the arms, but biserial at the extremity, which is 

 un additional proof how artificial is the old division of the Asterias 

 adojited by Mliller and Troschel. These tentacles are terminated by 

 a very small sucking disk which still further approximates Zoroaster 

 to Liiidia ; they are intermixed with small straight pedicellari^e 

 (pedicellaires droites). We may give the same name to some of these 

 organs disseminated between the dorsal plates. 



Synthetic Starfish. — At p. 448 was noted an interesting form of 

 starfish, apparently bridging over the gap between the Stellerida and 

 the Ophiurida, which had been described by Mr. W. Percy Sladen. 

 M. E. Perrier now describes * a still more remarkable type obtained 

 from the Gulf of Mexico during the dredging operations above 

 referred to. 



This starfish is very delicate in its structure ; it has a rounded 

 disk distinctly separated from the arms, as in the Ophiurida, and the 

 arms are elongated, flexible, and furnished with lateral rows of spines, 

 thus increasing the general resemblance to the Brittle-Stars. But 

 there are twelve arms, whilst no known Ophiurid has more than 

 seven. The description of the disk is very curious, and nothing like 

 it is known elsewhere among starfishes. It is flattened, very thin, and 

 quite destitute of any regular skeleton, the dorsal membrane being in 

 fact literally a circular membrane stretched upon the ring formed by 

 the basal ossicles of the arms ; it is membranous and transparent, and 

 so close to the buccal membrane that the stomach has only a space 

 about equal to the thickness of a sheet of paper in which to lodge. 

 M. Perrier very justly asks what can be the usual food of "u animal 

 with such a digestive cavity ? The dorsal skeleton is, however, repre- 

 sented by scattered perforated calcareous plates, each bearing a small 

 spine. Through the membrane the circular canal surrounding the 

 mouth, and the ambulacral vessels starting from it, may be recognized, 

 but no csecal prolongations of the stomach into the arms were to 

 be detected. The arms possess a double row of ambulacral tubes, 

 but no genital glanfls could be discerned in them. The skeleton 

 of the arms consists of four rows of pieces, two of which form a dorsal 

 ridge, and partially cover the others, which are placed on each side, 

 and each of which bears a median spine enclosed in a soft sheath, 

 clavate, and bearing at the apex a tuft of pedicellari^, the latter being 

 of the kind denominated " pedicellaires croisees " by M. Perrier, and 

 peculiarly characteristic of the Asteriadse, the most typical group of 

 the true starfishes. The lateral plates form the borders of the ambu- 

 lacral groove, in which the ambulacral vessel rests exactly as in the 



* Loc. cit. See ' Pop. Sci. Eev.' (1880) pp. 380-1. 



