GENEEA AKD GEOTJPS OF THE ECHIITOIDEA. 275 



Echini,' pi. xxiii., the distinctions between tliem and those of Loven 

 seem remarkable. The apex is very excentric in front in the speci- 

 mens figured by Agassiz, the ambulacra are double near the apex, 

 the apical system is longest transversely, and the fifth basal is 

 visible. The shape of the mouth and of the anus, the visibility 

 of the pentagonal fasciole from below, and indeed the shape of 

 the test as a whole differ in the two forms. These are startling 

 differences to find in the same species. 



Agassiz mentions Palceotropus Thomsoni, and the diagnosis he 

 gives (' Blake Echini,' p. 55) shows that the form differs most 

 strikingly from all the other specimens ot Palceotropus. It is 

 closely covered with uniform tubercles on the abactinal side, and 

 has a proportionally greater number of coronal plates and a 

 high test with a keeled posterior interradium. The apex is 

 more posterior than in P. Josephines. He remarks that the 

 species " differs most strikingly from all the other species," and 

 refers to the bare posterior lateral ambulacra actinally, the very 

 elongate plastron, and the longitudinally elongate fasciole. No 

 illustration is given of the species, which was dredged from a 

 depth of 233 fathoms between Bermuda and the mainland. 



Another species was described by A. Agassiz in the Eeport 

 on the ' Challenger ' Echini, p. 158 (1881). In this, Palceotropus 

 Loveni, there are three generative pores and no fifth basal ; the 

 mouth, anus, fasciolar space, ornamentation, and the shape 

 differ from those of the original type; moreover there is a 

 wide anterior ambulacral groove drawn on plate xxi. fig. 6. 

 As this form came from the Philippines, a considerable departure 

 from the type was to be expected. Considering the history 

 of Hemiaster, it may belong to Loven's genus. 



Grenus Homolampas, A. Agassiz, 1872-74, Revision of the JEeMni, 

 pp. 347, 562 ; 1881, Report on the ' Challenger ' Echini, 

 p. 163 ; 1883, Beport on ' Blahe ' Echini, p. 87. 

 Syn. Lissonotus, A. Ag., 1869. 



Test large, elongate, cordiform, notched at the anterior mar- 

 gin considerably, and less so posteriorly ; depressed, longer than 

 broad, broader than high, and broadest and highest in the 

 anterior third. Very flat actinally, but with a keel in the median 

 line of the plastron. Highest anteriorly, where it is boldly 

 curved and precipitous, and sloping gradually posteriorly to the 

 short truncation. A broad anterior groove. 



18* 



