238 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



UNSTALKED CRINOIDS. 

 Heliometra rhomboidea (P. H. Carpenter.) 



This species was met with during the "Albatross" Eastern Pacific Expedition 

 at three stations near the Central American coast ; in all, four specimens were 

 secured, a calyx without arms or cirri (Station No. 4622), an immature specimen 

 and fragments of the arms of an adult (Station No. 4621), and a nearly perfect 

 specimen, but with only three cirri remaining (Station No. 4630). 



The specimen from Station No. 4630 expands 300 mm. The three remaining 

 cirri have fifty-four, fifty-two, and forty-eight segments respectively. The first 

 pinnule is 18 mm. long, with fifty-five segments, the second 22 mm. long, with 

 fifty-three, and the third 17 mm. long, with thirty-one. The second pinnule is 

 rather stouter than the first, the segments proportionately slightly longer ; the 

 third pinnule has the segments considerably elongated ; the two following pin- 

 nules are about the length of the third, but have twenty-five to thirty segments, of 

 which the terminal five or six are short, the others elongated. In the ten arms 

 syzygia occur in all cases in the third brachials, nine times in the eighth (once in 

 the ninth), once in the twelfth, twice in the thirteenth, five times in the fourteenth, 

 and once in the fifteenth (the tenth arm is missing). Distally syzygia occur forty 

 times at intervals of three brachials, eight times at intervals of four, and six times 

 at intervals of two. 



It will be seen that this specimen is almost identical with the one described by 

 Dr. Hartlaub from the bay of Panama. I quite agree with him that it must be 

 referred to H. rhomboidea, in spite of the fact that the species is not known be- 

 tween Panama and the Straits of Magellan. It is quite distinct from any of the 

 numerous forms found along the shores of the north Pacific which were unknown 

 at the time Dr. Hartlaub wrote. 



The detached arms from Station No. 4621 are somewhat different from those 

 of the specimen just noticed. The brachials are quadrate, all longer than wide, 

 becoming elongate distally and overlapping, the distal border finely serrate; a 

 close comparison shows that the brachials overlap rather more than do those of 

 the other specimen, and the arms are therefore more rough, while the two proximal 

 pinnule segments are proportionately somewhat larger (the first shorter and more 

 oblong) and more expanded laterally, the second being more distinctly trapezoidal. 

 The distal intersyzygial interval is decidedly more variable, being in four cases of 

 two brachials, eight cases of three, thirteen of four, seven of five, six of six, four 

 of seven, one of eight, and one of nine. These differences, however, are of 

 minor systematic importance in this species, and, in fact, in many speices of 

 Heliometra, although in others they may be of considerable value, and I have 

 no hesitation in assigning this specimen, as well as the previous one, to H. 

 rhomboidea. Station No. 4621 also yielded a small specimen having an expanse 

 of 150 mm. The cirri have thirty-six segments, the third syzygy is usually in the 

 fourteenth brachial (but once in the fifteenth), and the distal intersyzygial 

 interval is three to five (usually three) segments. It will be seen that this 



