AUT. 21. PARASITES OF SHARKS AND SKATES LINTON, 95 



There is a singularly close agreement between the plan of hooks 

 on the proboscides of this species and that found in Rhynchohoth- 

 o-ium uncinatum from Vidpecula marina. In each there is a basal 

 portion which is devoid of hooks. This is followed by a collar-like 

 cluster of relatively long hooks. This cluster does not completely 

 surround the proboscis, but is on the side which corresponds with 

 the periphery of the scolex. This is the position in which the hook? 

 would be most serviceable as hold-fast organs. These large hooks 

 are followed by very small, closely set hooks, which, in turn, are 

 soon followed by longer, for the most part, slender hooks. Two 

 vertical rows of stouter hooks lie on the peripheral side of the probo- 

 scis (1901, figs. 257-260). One proboscis was seen which was more 

 than two- thirds of its length everted. It maintained a practically 

 uniform diameter throughout. 



Dimensions in balsam: Length of bothria, 2.80, breadth 2.03; 

 diameter of neck, 2.03; length of proboscis, 5.32; diameter of un- 

 armed, basal portion, 0.17; diameter of median region, including 

 hooks, 0.28, excluding hooks, 0.17; length of large basal hooks, 0.14, 

 of small hooks, in front of basal hooks, 0.03, of slender hooks, most 

 abundant kind, 0.10; length of contractile bulb 2.10, diameter 0.56. 



TETRARHYNCHUS PALLIATUS, new species. 



Plate 8, Figs. 81-84. 



Tetrarhynchus hisulcatus Linton, MacCallum. Studies in Helminthology, 

 vol. 1, No. 6 (1921). p. 206, fig. 105. 



Scolex. — Concave in front; bothria long oval, bluntly pointed; 

 neck portion short, subcylindrical ; collar ample, flaring at posterior 

 border; bulbs reaching almost to beginning of strobile; proboscis 

 sheathes with about one spiral at junction with bulb, then nearly 

 straight; retracted proboscides reach nearly to bulb; proboscides 

 cylindrical, hooks of nearly uniform size and shape, increasing in 

 size slightly toward tip, relatively stout, strongly recurved, about 

 six showing in single spiral on one side, apparently about twelve 

 vertical rows; collar of scolex more than one-third length of entire 

 scolex, considerably wider than anterior portion of strobile, especially 

 in specimens which have been more or less compressed. 



The concavity at the anterior end, and the ample, flaring collar 

 are distinct specific characters. 



Strobile. — In uncompressed specimens, the strobile is nearly linear, 

 under pressure, increasing in breadth slightb/ but uniformly toward 

 the posterior end; free, ripe proglottides not seen. The first prog- 

 lottides are enclosed in the collar of the scolex and are very short. 

 They increase in length very slowly; posterior margins slightly pro- 

 jecting, thus giving to the lateral margins of the strobile a more or 

 20183— 2.5— Proc.N.M.vol.64 .30 



