132 THE VOYAGE OF H.M.S. CHALLENGER. 



cioles, and the large size and small number of the coronal plates in lioth areas, Ijoth on 

 the actinal and abactinal sides of the test, also show the structural affinities in the 

 direction of the Ananchytidse and Galeritidse. 



It is remarkable that it is among the Dysasteridse ' to which the Pourtalesiee are in 

 many respects most closely allied, that we also find a very great diversity in the outline of 

 the test; many species of the CoUyritidEe, such as Dysaster calceolatus, resemble closely 

 our recent Echiyiocrepis ; others, like Colly rites jaccardi, Des., remind us of Urechinus. 

 On the other hand such genera as Archiacia, Infidaster, Grasia, and Metaporhimis, 

 among the extinct genera, show quite as great diversity in shape as we find between 

 Pourtalesia, Oystechinus and Spatagocystls among the deep-sea types of Pom-talesise. 



It is interesting to note the general character of the pedicellarise. Among the 

 numerous genera of Pourtalesise there is no group of Echinids in which we find so many 

 difi"erent kinds, and theii- structure Hke that of the spines and of the difi"erent parts of 

 the test points to the most varied systematic affinities. We find among these the large- 

 headed pedicellariffi (PI. XLV. fig. 48) of Pourtalesia (PI. XLV. figs. 28, 36), of Cyst- 

 echinus, of Spatagocystis (PI. XLV. fig. 39), of Genicojmtagus (PL XLV. fig. 21), the 

 type of Spatangoid pedicellariaj which most closely resembles that of the large-headed 

 pedicellariae of the Echinidse and Echinometradse'. 



We next find the Spatangoid type (PL XLV. figs 20, 20') which in this group seems 

 frequently modified to assume the more Echinid-like type, of which Pseudoholetia is an 

 example (PL XLIV. fig. 38), of having one or two large hooks terminating the more or 

 less narrow prong of the valves as in Pourtalesia (PL XLV. figs. 46, 47, 49, 56, 57, 58). 

 Or else we have the extremity of the valves varying from the Spatangoid type in becom- 

 ing more or less cup-shaped (PL XLV. fig. 41) with strong serrations (PL XLV. fig. 43, 

 Echinocrepis) approaching somewhat the regular crescentic serrations so characteristic of 

 the Clypeastroids, and which is still more markedly Clypeastroid in Aceste (PL XLIV. 

 fig. 47). In Cystechinus, and specially in Pourtalesia proper, these Clypeastroid 

 like pedicellaria3 are very characteristic of the type and indicative of one of the most in- 

 teresting of the affinities of this Spatangoid group of Echinids, an affinity fully borne out 

 by a comparison of other structural features. It is specially interesting to note in this 

 connection that in Echinolampas (PL XLIII. figs. 3, 4 ; PL XLV. figs. 41, 43) these 

 Clypeastroid like pediceUarise also occur. 



Pourtalesia. 



Pourtalesia, A. Agassiz, 1869, Bull. Mus. Comii. Zool., vol. i. 



In the genus Pourtalesia proper, as 1 have retained it here, there are two groups of 

 species readily distinguished from the character of the test ; these I was at first inclined 



1 The spines of the Dysasteridse, which have been figured by Coster and De Loriol, are similar to those of the 

 Pourtalesiee. 



