Haplodiscus Piger; a new Pelagic Organism 
from the Bahamas. 
By 
W. F. It. Weldon, M.A., 
Fellow of St. John’s College, Cambridge, Lecturer on Invertebrate 
Morphology in the University. 
With Plate I. 
I propose the name Haplodiscus for a small pelagic 
organism occasionally found in the tow-net near the island of 
New Providence, Bahamas. 
The specimens found by me were collected between the 
months of July and November, about fifteen specimens in all 
having been obtained during this period. As I employed a 
great part of my time during my visit to the Bahamas in 
using a tow-net, the creature may fairly be called rare. 
The general appearance of Haplodiscus, as seen under a 
simple lens, is shown in fig. 1. The body is ellipsoidal in 
outline, the antero-posterior diameter being the shortest. In 
an average specimen the long diameter measured 1"3 mm., the 
short 1*1 mm. The dorsal surface of the body is slightly 
convex ; the ventral surface is flat when the animal is at rest, 
but capable of becoming concave as a consequence of muscular 
contraction. It is by producing a concavity on its ventral 
surface that the animal slowly and sluggishly moves through 
the water ; this mode of progression, together with a general 
superficial likeness to a Protozoon, producing a strong re- 
semblance to the Lcptodiscus medusoides of R. Hertwig. 
The internal anatomy can only be properly made out by 
VOL. XXIX PART 1. NEW SER. A 
