Io6 ECHINOIDEA. II. 



Though no more recent species of Honiastrr have beeii described ( — except the Abatus-^^^zx^s 

 wrougly referred to this genus — ) there is reason to discnss one more species in this connection, viz. 

 the. Periasier femds A. Ag. described and fignred in the ' Panamic Deep-Sea Echini» p. 209, PI. 103, 

 figs. 5 — 7, 104, 105, figs. 1—3. At the first glance on the fignres, especially on PI. 104, one is strnck by 

 the close resemblance of this species to a Ilmiiastcr, and a stndy of the details of the strncture of 

 the test can only strengthen the first impression. Above all the ethmophract apical system, so closely 

 Hke that of Hemiastcr biifo. as pointed out by Agassiz, but also the total want of a latero-anal 

 fasciole, tend to show that it is really a Hrmiastcr. Further the elongate labrum, reaching to the 

 middle of the second anibulacral piates of the adjoining series, the condition of the petals and the 

 shape of the test, recall very much H. cxpcrgifus. Also the pedicellariæ point decidedly towards 

 Hemiaster, as I can state having examined a specimen ( Albatross? St. 3398) in the U. S. National 

 Museum. The globiferons pedicellariæ resemble those of //. expergitus, though more coarse (PL XV. 

 Fig. 33), the terminal opening is rather wide and surrouuded by teeth as in expergitus; thev are, un- 

 fortnnately, all somewhat broken in the only specimen found. The blade is a rather wide tube, with a 

 comparatively narrow (glandular) space continuing down into the basal part. The stalk is thick and 

 compact, but without distinct thickening or projections. The tridentate pedicellariæ are of two kinds 

 of different size; the small form fPl. XV. Fig. 49) is very Hke that of expergitus, onl>- the skin is much 

 thicker, especially the neck is very conspicuous; the large form (head ca. 07'""') differs from that of 

 expergitus in the outer part of the blade being more ronnded (PI. XV. Fig. 4). Specimens of this kind 

 of tridentate pedicellariæ not larger than the small form may be found, which shows that they are, 

 indeed, two separate forms of pedicellariæ. Rostrate and ophicephalous pedicellariæ were not found; 

 the triphyllous pedicellariæ do not differ from those of expergitus. Spicules as in expergitus. 



From what has liere been pointed out I think it evident that this species really belongs to 

 the genus Ilenuaster, the absence of a latero-anal fasciole especially being a character non-conformable 

 with referring it to the genus Periaster. Through the prominent labrum and narrow plastron, as well 

 as through the pedicellariæ and the general shape of the test (especially the outline in profil — comp. 

 PI. II. Fig. 20 with PL 104. Fig. 3 of the «Pan. Deep-Sea Ech.») Hemiaster tenuis (A. Ag.), as its name 

 must be, is easily distinguished from its nearest relation, //. expergitus (incl. gibbos2(s). 



It may be appropriate to give in this connection sonie remarks on Periaster liinicola, the only 

 other recent species hitherto referred to the genus Periaster.^ — The tnbercles along the anterior ani- 

 bulacrum increase in size towards the apical system, the largest tubercle and longest spine being tliat 

 nearest the apical system, as is also the case in Hemiaster expergitus. The apical system (which is not 

 represented in a sufficiently detailed manner in the otherwise beautiful Figure 6. PL XXVI of the 

 «Blake»-Echini) is .said in the Panamic Deep-Sea Echini p. 211 to be IfciiiiasterASkft^ though it has 

 only two genital pores. In the specimens in hånd the apical system is not very He))iiasfcr-\\]^it\ it is 

 ethmolytic, the madreporite separating also the posterior ocular piates (Fig. 21). This is evidentl)- also 

 the case in the figure quoted of the <;Blake»-Echini, though the sutures are not distinct. This species 

 is thus not in accordance with the diagnosis of the genus Periaster given by Pomcl (Classif. mé- 



I In A. Agassiz aiul H. Lym. Clark: Preliminaiy Report 011 the Echini coUected, in 1902, aniong the Hawaiian 

 Islands (BuU. Mus. Comp. Zool. I,. 1907), a new species of Periaster, P. maximus^ is described (p. 259). 



