NORTH PACIFIC OPHIURANS IN NATIONAL MUSEUM CLARK. 3 



tempt in this report to present an improved classification of the 

 Ophiuroidea, but it is at least permissible for me to make this protest 

 against the one which I am obliged to use. 



One of the principal reasons why the ophiurans are such a difficult 

 group to classify is found in our ignorance of their growth changes. 

 It has been recognized for some time that the number of arm spines 

 and oral papillae often increases with age, and Lyman called attention 

 in the Challenger report to other changes which he had noted, partic- 

 ularly in OpJiiactis and Ophiacantha. What is needed is a detailed 

 study of the growth changes in some one species of each family, bring- 

 ing out just what characters are evidences of immaturity. Ludwig, 

 in his Jugendf ormen von Ophiuren ' has made an excellent beginning 

 for a number of the viviparous species, but such work needs to be car- 

 ried much further. 



The study of this collection has satisfied me that Jackson's 6 law of 

 "localized stages" is a very real help in determining the possible rela- 

 tionship between small and large individuals of the same genus. For 

 the ophiuran arm reveals at and near the tip the characters of youth 

 and one can thus compare the base of the arm of a small specimen 

 with the middle or tip of the arm of a large individual with most sug- 

 gestive results. The extent to which the youthful characters are 

 localized varies with different species, but as a rule they are suffi- 

 ciently clear to make comparisons conclusive. 



Another interesting matter is variation in the extent of calcification 

 or of resorption of calcareous matter, which many species of ophiu- 

 rans, especially in the family Amphiuridse, reveal. As a rule, calcifi- 

 cation progresses more or less steadily from youth on, so that old in- 

 dividuals are much heavier and more solid, relatively, than young 

 ones. This is especially true in the Ophiolepididae, where the increase 

 may be shown not only by the heavier plates but by lumps and swell- 

 ings upon the plates, wanting or only faintly indicated in young individ- 

 uals. In the Amphiuridae and a few species of OpJiiura, however, it is 

 often true that resorption exceeds the deposit of lime, and as a result the 

 old individuals may have most of the disk scales and even the margins 

 of the basal arm plates extensively, if not completely, resorbed. In 

 such species, while a small specimen will have the disk well covered 

 with scales, both above and below, larger individuals have the inter- 

 brachial spaces below entirely bare, and old ones may have no disk 

 scales at all except just around the radial shields. Other factors than 

 that of age appear to enter into the matter, however, for individuals 

 of the same size may reveal great differences in the amount of calcifi- 

 cation. It seems quite possible that external factors, such as food, 

 composition of the sea water, character of the bottom, etc., may be the 



a Sitzungsb. Akad. Wiss. Berlin, vol. 14, 1899, pp. 210-235. 

 &R. T. Jackson, Mem. Boston Soc. Nat. Hist., vol. 5, 1899, p. 4. 



