I7 o ECHINOIDEA. II. 



median space is very conspicuous. Also the interambulacra are represented in this figure as having 

 no naked median line, whereas Tr. Bartletti really has a conspicuous naked median line in the inter- 

 ambulacra. — A specimen from the «Blake» St. 272, examined in the Museum of Yale College, also 

 agrees with the specimens in the U. S. National Museum, not with the said figure PI. II. 16. It thus 

 seems that the said figure has been made from another species, the figure being otherwise evidently 

 very carefully drawn. In case the figure really represents Tr. Bartletti correctly Tr. annulata must 

 be retained as a distinct species, to which the specimens seen by me in the U. S. National Museum 

 and the Museum of Yale College would have to be referred. 



To the description of the species may be added, besides the peculiar feature already pointed 

 out in the description of Tr. annulata that the radioles are spinous almost exclusively along their 

 upper side, that the actinal radioles are almost smooth, slightly flattened, but not serrate along the 

 edge, and not widened towards the point. The primary ambulacral spines are narrow and pointed, 

 only about half as large as the spines round the radioles, not nearly of the same size as the latter, 

 as is stated in the description in the <Blake»-Echinoidea. The inner ambulacral spines have a distinct 

 «ampulla» on the upper edge. The differences in the globiferous pedicellarice of Bartletti and annulata 

 shown in Part I. PI. X. Figs. 22, 31 and Figs. 23, 30 are certainly not sufficient for maintaining two 

 species, the more so as this species has been shown by Agassiz and Clark in the recently published 

 work on the Cidaridtz 1 to vary considerably in regard to the pedicellariEe. — As regards the genus 

 Tretocidaris which is rejected in this latter work I cannot take up the discussion here, but I hope to 

 have occasion soon to rediscuss the matter. 



Hygrosoma Petersii (A. Ag.). Several specimens were taken by the «Thor in 1906 at 49° 20' 

 Lat. N. 12 39' Long. W. 1520 M. To this species must also be referred the specimens from the Bay of 

 Biscay mentioned by Koehler (Echinod. du < Caudan . p. 92) under the name of Phormosouia lucii/e/i- 

 tum, as Professor Koehler informs me in a letter. 



Sperosoma Grimaldi Koehler. In Part I (p. 77. PI. IV. Figs. 4, 5) was described and figured a 

 young specimen of this species, 27""" in diameter. The figures (which were not drawn by myself) 

 are, however, too little detailed and do not show the structure of the test exactly. As it will be of 

 considerable interest to get some knowledge of the development of this very interesting genus, I give 

 here some detailed figures of parts of the test of the specimen mentioned. It would, of course, have 

 been desirable to have some younger stages, but such have not yet been found, and the present speci- 

 men is still young enough to be of value for the study of the development of this form. 



The ambulacra on the actinal side already show the structure typical of the genus, the larger 

 primary plate of each set being divided into an outer, smaller, pore-bearing plate and an inner, larger 

 one without pore; this is the case also with those nearest the actinostome. As is well known the 

 inner ambulacral plates with the growth of the specimen pass on to the buccal membrane and there 

 develop into very broad, but short plates, which cover the whole buccal membrane. In the small 

 specimen 4 such plates, besides the inner one, the true buccal plate, are counted in each series; in a 



1 A. Agassiz and H. Lyman Clark: Hawaiian and other Pacific Echini. The Cidarida;. Mem. Mus. Comp. Zool. 

 XXXIV. 1. 1907. — This work was not received before most of the present work was printed, so that I was unable to take 

 it into consideration in my introductory remarks. 



