[85] 



NOTES ON ENTOZOA OF MARINE FISHES. 



803 



or posterior, plate is of about the same thickness as the anterior one ? 

 and, in the living specimen, is nearly circular, and bears four supple- 

 mental disks (auxiliary acetabula), which are nearly equidistant on the 

 margin. In the alcoholic specimens, however, the posterior plate is 

 found to be somewhat smaller than the other. Its margius are entire, 

 smooth and quadrangular. The largest sides of the quadrangle cor- 

 respond to the lateral sides of the strobile, aud the supplemental disks 

 are at the angles. In some cases the angles which bear the supple- 

 mental disks are slightly prolonged. 



The supplemental disks are directed sometimes forward, sometimes 

 backward. Their usual direction is probably outward, or at right 

 angles to the axis of the body. The diameter of a single disk, measured 

 in an alcoholic specimen, is .l mm . 



The neck, or anterior part of the body, is attached to the posterior 

 side of the disk-shaped head, like the petiole of a peltate leaf to its 

 blade. 



Segments begin about l mm , or less, back of the head. The first dis- 

 tinct segments are broader than long. The segments are, at first, rather 

 flat, squarish or rectaugular, with parallel sides and sharp augles, but 

 as the reproductive organs begin to mature, the segments become 

 rounded and somewhat thickened, giving a moniliform outline to the 

 strobile. The posterior segments are considerably elongated, sometimes 

 bacilliform, rounded at the angles and slightly constricted at the ends, 

 at other times elongated and rectangular. 



Reproductive apertures marginal, a little in front of the middle of the 

 segment. Cirrus bulb large, oval, with anterior prolongation. Cirrus 

 echinate. 



Habitat. — Trygon centrum, spiral valve, July 29, 1886, July 10, 1887, 

 and August 1, 1887. Wood's Holl, Massachusetts. 



I have obtained this entozoon on three different occasions, each time 

 from the spiral valve of the sting ray (Trygon centrum), and each time 

 but few specimens. The first lot contained but one specimen; the 

 others four or five each. 



The following measurements were made on living specimens, one from 

 each lot : 



Dimensions. 



Length .1 



Diameter of head 



Thickness of head 



Diameter of neck 



Distance to first distinct segment. 



Length of first segment 



Breadth of first segment 



Length of last segment 



.Breadth of last segment 



Number of segments 



No. 1. No. 2. No. 3 



mm. 

 8.20 

 .90 



.16 



.04 

 .16 

 .85 

 .30 



mm. 

 12.50 

 .68 



.12 

 .20 

 .02 

 .12 

 1.50 

 .32 

 60 



mm. 

 14.00 

 .80 

 .40 

 .14 

 1.00 

 .10 

 .18 

 .80 

 .26 



