SYSTEMATIC CLASSIFICATION OK l-( HIM 21.', 



on account of differences in spicules of the tube-feel whirl, an- vi-ry law and ,^-uliur, HIM! on 

 differences of the pedicellariae. It differs from the Kchinometndae al-o i,, that tin- ocular* 

 enter the periproct in the sequence I, V, IV (p. 1 13), not V, I, I \ . M in that family Th- mo* 

 important character, however, is that the teeth arc keeled and rpiphys.^ narrow, not m .-..in, K 

 in suture over the foramen magnum (Plate 4, figs. 8-10). Other important ix-niliariti,-* exist 

 as described (p. 186). The character of the lantern places this genus and family a> a member 

 of the Stirodonta. Its affinities are nearest to the I'liym.^omatidae a- indicate,! l>y pur- 

 from the dorsal tips of the pyramids, which support the teeth Plate J. figs, s 111). Th,. ambu- 

 lacral plates are composed of three elements each, and where fully developed, a- at the mid- 

 zone, four or five plates are combined and grown over by a large primary tubercle, a very strik- 

 ing character. The periproct has numerous small plates, as in Phymosoma. The orular 

 plates of the bivium are typically insert in Slomopneusles variolaris, but I only or I. V. IV may 

 be insert as described (p. 113). Also, as an aberrant variation, three specimen- in a total of 

 64 have oculars I, V, II insert. This is an essential character of the Kchinidae and Strongylu- 

 centrotidae, and suggests a connection between the families. The small suranal plate of <;iijil- 

 cidaris crenulare, as figured by Mr. Agassiz (1873, Plate 7a, fig. 8). suggest., the sum- affinity, 

 and it seems that in one of these two families may lie the ancestral stock <>i tin- Kchinidae and 

 allies. 



Of the Arbaciidae the most striking feature is that there are only four, or five, nearly equal 

 plates in the periproct, a feature otherwise known only in Parasalenia. Another important 

 feature not so readily ascertained is the retention of the primordial interambulacral plates in 

 the basicoronal row, as pointed out by Mr. Agassiz (1904, p. 54). A third unusual character 

 is that ocular plates, when they enter the periproct, do so in the sequence V. I. IV p. 158). 

 This is known elsewhere only in the Echinometridae, as here shown. The auricl .|ely 



separate styloid processes (text-fig. 227, p. 193) or slightly arched and joined by suture 

 228). Tube-feet are dorsally modified as ambulacral gills in Arbacia (A. Agassiz, 1872, p. 204). 

 In the genera Habrocidaris and Podocidaris, as shown by A. Agassiz and Clark 1 1908, p. 77), 

 and Pygmaeocidaris, as shown by Doderlein l (1906), the primordial interambulacral plate is 

 retained as in Arbacia. 



The suborder Camarodonta may be considered the most specialized of modern regular 

 Echini on the basis of the lantern, and also in various genera by the sculptured test, the degree 

 of specialization of the ambulacrum, peristome, perignathic girdle, or the elliptical form through 

 a sidewise axis. The essential feature is the fact, that while the teeth are keeled as in the last 



1 Doderlein figures (190G, p. 184, fig. 36e) a third median pl:il- in the third coronal row of t'yicmarocidaris. As this 

 genus so closely resembles Habrocidaris, in which there i* a im-diaii tubercle but no median third plutp, it is powihlr that 

 Doderlein was misled in introducing thesutures of I his plate, a point difficult to ascertain in such a small specimen (4.8mm.) 

 as he had. If Doderlein is correct, it is a unique ease in the Ontrwhinoida. 



