BY T. HARVEY JOHNSTON AND 0. W. TIEGS. 87 



C. a. Minute, very robust worms, in which the yolk system has, in addition to the 

 ■ordinary transverse duct anterior to ovary, at least one posterior transverse 



duct which communicates with the intestine Protogyrodactylidae 



b. Slender worms, in which this character of the vitelline system is quite 

 absent Gyrodactylidae 



Family I. PROTOGYRODACTYLIDAE, n. fam. 



These are primitive, minute Gyrodaetyloidea, about as broad as long, with 

 a greatly developed clasping disc bearing two paii-s of relatively very large 

 clasping hooks and numerous minor hooks which are rather larger than usual. 



The cephalic glands open to the exterior by well-defined head-organs. There 

 is a prominent phaxynx. The intestine is bifui-cated, the limbs ending blindly or 

 uniting posteriorly. Intestinal caeca absent. 



Neither testis nor ovary is branched. There is no vagina. The uterus is 

 very short. The cirrus is a simple chitinous tube, enclosed in a ciiTUS-sac. The 

 yolk system is vei7 remarkable in that it consists of numerous long thin "yolk- 

 tubes," aiTanged in two sets, the one anterior, the other posterior, to the ovai-y. 

 The transverse yolk-ducts so formed are connected by a longitudinal median yolls- 

 duet which opens into the ootype. The posterior transveree yolk-duct has a 

 distinct connection with the intestinal limbs. 



Found, so fai', only on the gills of freshwater fishes. 



Type genus, Protogyrodactylus J. & T., 1922. 



The family also includes Trivitellina 3. & T. Should the discovei-y of other 

 genera belonging to thei family necessitate its subdivision, then these two, owing 

 to their close relationship would be included in the same subfamily, Protogyro- 

 dactylinae. 



1. Protogyeodacttlus, n.gen. 



Protogyrodactylidae, slightly broader than long; the clasping disc very broad, 

 not sharply marked off from the body, strongly "padded," bearing four very 

 large, and twelve minor hooks, the latter rather larger than usual. A veiy short 

 oesophagus present; the limbs of the intestine not united posteriorly. Four eyes 

 present, lying above the brain. A single posterior transverse yolk-duct con- 

 nected with the intestine. 



Found on the gills of freshwater fishes. 



Type species, Protogyrodactylus quadratics J. & T. 



Pbotogybodactylus quadratus, n.sp. (Plate ix., Fig. 1-5; x., Fig. 6.) 



The worm is short and thickset, a little broader than long, and about three 

 times as long as thick. Its length is about .23 nun. On account of the wing- 

 like expansions of the sides, the head is distinctly mai-ked off from the body 

 of the animal. Two distinct head-lobes ai'e developed on it. 



The disc is very prominent, but is not sharply marked off from the rest 

 of the body, as is indicated in the section on Plate ix., figure 3. It is provided 

 with four hooks, two of which are very large, powerful and strongly curved, 

 the other two somewhat smaller, straighter and more slender. The bases of the 

 hooks are supported by a transverse chitinous bar, aiiiculating with the ends of 

 which are (1) a pair of small pieces of chitin, to which the powerful muscles 

 of the disc become attached in part, and (2) a pair of larger inwardly-directed 

 chitinous pieces. There are also twelve minor hooks, rather larger than usual, 



