84 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



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

 tudinal horizontal. The sections were stained on the slide with Kleinenberg's hsematoxylon. 

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

 shrinkage in echinoderm tissue, which usually accompanies the unmodified paraffin 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 terms which are used synonymously in 

 the text of this paper in the description of the larvae. Those in the same line can, in most cases, 

 be interchangeably used. 



Dorsal-aboral-above-over. 

 Ventral-oral-below-under. 

 Anterior-forward-before. 

 Posterior-back ward-behind. 



In the drawings of the larva-, 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, this method seeming preferable 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 suggestions in methods of rearing larva' at the seashore. 



To Professor Brooks, 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 offered from time to time during the year. 



HISTORICAL SKETCH. 



The species of Ophiuran, Ophiura brevispina, the life history of which is the subject of this 

 dissertation, was first discovered and described by Thomas Say in 1825 (12). 



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

 probably best known at present by one of its synonyms, Ophiura olivacea, which was given to it 

 in 1865 by Theodore Lyman (S). In his earlier works Lyman distinguished between 0. olivacea 

 and 0. brevispina, but in his Challenger report on the Ophiuridce and Astrophytidce (9) 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 1S52 Ayers described the species under the name Ophioderma olivaceum in Vol. IV of the 

 Proc. Bost. Soc. Nat. Hist. 



Lutken also described it as Ophioderma 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 New England. 

 It has been taken from the following localities: 



1. Bahia, Brazil. 6. Beaufort, North Carolina. 



2. Port Antonio, Jamaica. 7. Old Point Comfort, Virginia. 



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 fathom. 



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

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



