50 Proceedings of the Biological Society of Washington. 



similar plates, the more distal of which lie about half way from the base 

 to the outer edge of the entire smaller portion as viewed laterally. On 

 both sides the surface is torn away in the angle between tlie outermost of 

 the vertical columns, and the uppermost of the horizontal rows. To the 

 left the horizontal rows terminate in a torn edge; to the right they become 

 lost in a maze of plates similar to those of the surface of the larger portion. 



Inner Structure of the Larger Part. — The larger portion is a completely 

 enclosed sac, showing no evidence of communication either with the 

 exterior or with the interior of the smaller portion. Within it I can find 

 nothing but a thick irregular lining of connective tissue, on the surface 

 of which is an elongate depression, evidently mistaken by Dr. Clark for 

 the lumen of a digestive tube. 



Inner Structure of the Smaller Part. — The interior of the smaller portion 

 is mostly occupied by gonads, lying along its longer axis. But I also 

 found a relatively large sac-like structure and part of another near the 

 broken end of the columns. 



Identification of the Specimen.— The features which offer the greatest 

 possibilities for the determination of the specimen are ( 1 ) the arrange- 

 ment of the plates on both the larger and the smaller portions, (2) the 

 character and distribution of the spines, and (3) the character and dis- 

 tribution of the pedicellarise. 



The pedicellarife are of the type found in the Brisingidse. 



The arrangement of the plates on the larger portion and the distribution 

 of the spines and of the pedicellarise on these plates, as well as the 

 character of the spines, are identical with the same features in certain 

 species of Brinnga. 



The arrangement of the columns of plates in the smaller portion, and 

 the character of these plates and of the spines which they bear, are 

 exactly duplicated in the arm bases of certain species of Brisinga. 



Furthermore the gonads, which are very B rising a-\\\iQ, lie in the same 

 relation to these plates that they do to the dorsal arm plates of the species 

 of Brisinga ; and the sac-like structures are very like the rather large 

 Brisinga ampullae. 



As all the tangible characters of the specimen are identical with com- 

 parable characters in the genus Brisinga, and are not duplicated in any 

 other genus of echinoderms, least of all in the echinoids and holothurians, 

 it seems evident that we are dealing with a large cyst-like outgrowth 

 from the base of a Brisinga arm. 



A large species of Brisinga, in its details agreeing perfectly with com- 

 parable features of the specimen, was taken at the same dredge-haul; 

 furthermore, many of the specimens of this Brisinga bore cyst-like out- 

 growths on the arm bases containing a curious type of degenerate mollusc. 



There can be not the slightest doubt that this supposedly anomalous 

 echinoderm type is merely a detached cyst, with part of the dorsal surface 

 of the arms and the underlying gonads, from the species of Brisinga 

 dredged at "Albatross" Station 3342, from which the parasite has been 

 removed. — Austin H. Clark. 



