84 MEMOIRS OF THE 2^ATI0NAL ACADEMY OF SCIENCES. 



microns in thickness -svere made in three planes, transverse, longitudinal sagittal, and longi- 

 tudinal horizontal. The sections were stained on the slide with Kleinenbekg's ha>matoxylon. 

 Other methods were tried, but none proved so satisfactory as the one just described. The 

 shrinkage in echinoderm tissue, which usually accomi)anies the unmoditied i)araffiu method, was 

 not to be seen in the tissue of these larva-, due, no doubt, to its unusual thickness. 



It has been thought best to make the following list of teims which are nsed synonymously in 

 the text of this paper in the descri^Jtiou of the larvie. Those in the same line can, in most cases, 

 be interchangeably used. 



Dorsal-aboral-above-over. 

 Yentral-oral-below-under. 

 Auterior-forward-before. 

 Posterior-back ward-beh i nd . 



In the drawings of the larv;i-, when the ventral side is up and the anterior end is nearest the 

 top of the page, then the reader's left is also left in the figure. 



For convenience in description, the various stages taken to illustrate the life history of the 

 species have been designated by letters of the alphabet, tiiis method seeming jtreferable to one in 

 which age is used as a distinguishing character, since the progress of development at any age 

 depends so intimately on the varying conditions of environment. 



I take this opportunity to acknowledge my indebtedness to Dr. C. P. Sigekfoos, at whose 

 suggestion I began the study of Ophiuran development. 



I was aided very materially while at the Fish Commission laboratory by Prof. H. C. Bumpus, 

 who placed at my disposal every facility for work at his command, and to him, also, I am greatly 

 indebted for many suggesticnis in methods of rearing larva^ at the seashore. 



To Professor Beook.s, under whose direction my work has been done, are due my warmest 

 thanks for the interest with which he has followed me in my studies and for the many valuable 

 suggestions he has ofl'ered from time to time during the year. 



HISTORICAL SKETCH. 



Tlie species of Ophiuran, Ophiiira brcrisphui, the life history of which is the subject of this 

 dissertation, was first discovered and described by Thomas Say in 182.") (12). 



Since this time the species has been rediscovered and renamed as many as three times. It is 

 l)robably best known at present by one of its synonyms, Ophiuru olivaeea, which was given to it 

 in 1805 by Theodore Lyman (8). In his earlier works Lvman distinguished between (). oUracea 

 and O. hrevisphia, but in his GhaUeiKjer report on the Ophiuridw and A.stroplii/tidn- (It) he places 

 the two species together as one under its earlier name, which, although less descriptive of the 

 species than that given by Lyman, it is probably best to retain. 



In 1852 Ayeks described the species under the name Ophioderma oUvaceum in Vol. IV of the 

 Proc. Bost. Soc. Nat, Hist. 



LuTKEN also described it as Opliioderma serpens in 1856. 



DISTRIBUTION AND HABITS. 



Ophiura brevispina is a very widely distributed species, it having been reported from points 

 along the Atlantic coast from Brazil to Xew England. 

 It has been taken from the following localities: 



1. Bahia, Brazil. G. Beaufort, North Carolina. 



2. Port Antonio, Jamaica. 7. Old Point Comfort, ^'irginia. 



3. St. Thomas, Bahamas. 8. Sag Harbor, New York. 



4. Cape Florida, Florida. 9. Dartmouth, Massachusetts. 



5. Tortugas. 10. New Bedford, Massachusetts. 



11. North Falmouth, Massachusetts. 



That part of North Falmouth Harbor which is inhabited by the species is very shallow, its 

 depth at low tide not exceeding 1 lathom. 



The bottom is covered witli a mat of living and dead grasses and alga-, and in this tangle 

 the ophiuraus live, together with a great variety of crustaceans, niolusks, and worms. 



