1911] Watson: The Genus Gyrocotyle. 387 



spines, frequently referred to in the preceeding discussion of 

 the literature of the subject. In G. fimbriata, the spines are 

 arranged in a definite pattern, from which there is no great 

 amount of individual variation, though the number of spines 

 varies considerably. At the anterior extremity, on the lateral fin 

 on each side of the acetabulum are two groups of large spines 

 (pi. 36, figs. 22, 23). They are arranged in five rows, two each 

 on the dorsal and ventral surfaces and one row on the margin. 

 There are from five to seven spines in a row, from 20 to 30 in 

 each group. Here, as elsewhere, the spines are borne on rounded 

 papillae, which are in this region of greater size than elsewhere 

 on the body, except around the "neck" of the rosette. The 

 papillae extend back along the lateral fin to the beginning of 

 the lateral folds, but bear spines only at the region shown in 

 the figure, at the level of the posterior half of the acetabulum. 

 In addition to these large spines, of the shape shown in fig. 28, 

 there are a number of very much smaller, less definitely shaped 

 spines (pi. 37, fig. 32), in among the larger ones. 



There are no spines on either surface, throughout the length 

 of the body, back to the posterior border of the receptaculum 

 seminis. Here on the ventral surface two groups of spines appear, 

 near the base of the lateral folds, extending backward in con- 

 verging lines toward the canal opening. They flank this opening, 

 increasing in number and size, and spread out posteriorly on the 

 surface of the neck of the rosette in its median half. At the 

 posterior border of the neck they extend laterally, passing around 

 to the dorsal surface. On the extreme lateral margins of the 

 ventral surface appear two groups of spines, which pass over on 

 the dorsal surface, forming with the ring above described a belt 

 of spines on the dorsal surface of the neck. The number and 

 direction of these spines is shown in the figures (pi. 34, figs. 

 10, 12). 



In G. urna (var. ?) the distribution of spines (pi. 36, fig. 24; 

 pi. 34, figs. 11, 13) is markedly different. The ventral surface, 

 to the level of the uterus opening, is thickly set with large 

 spines ; there is no special pattern in the arrangement about the 

 neck, there being six or seven irregular rows of spines, encircling 

 the base of the rosette. On the dorsal surface the spines are 



