1874.] 173 [Garman. 



That it acts as a forcing or squirting apparatus is evident from the 

 fact that the cavity upon the ventrals, containing the muscular gland, 

 fills so readily with the sperm when the claspers are erected, and 

 that its contents are expelled, upon contraction of the muscles 

 around it, with such certainty to their ends, when restored to their 

 normal position. 



An attempt to use the livers as a means of determining the species 

 fails, because of the great amount of variation in volume and size 

 in the same species at different seasons. They seem to be smallest in 

 the females about the time of laying the eggs, probably on account of 

 a greater demand for their store of oil at that time. The position 

 and extent of this organ in these ribless animals, suggests that it 

 serves an important purpose, as it may. act by its mere presence as a 

 pad or cushion to soften the effect of hard knocks upon the more 

 tender organs it envelopes. 



It is found necessary, from the confusion existing in the literature, 

 to redescribe each species of our representatives of the genus Raja. 

 The grand collection in the Museum of Comparative Zoology affords 

 the means of doing this with some degree of readiness. In certain 

 respects, all of our skates agree in the general shape of the body, the 

 armature on the dorsal surface, and the position of the eyes, spiracles, 

 mouth, nostrils, and gill- openings. There are other particulars in 

 which they differ to a greater or less extent, as in size and outlines, 

 in shape and size of claspers, in the number, shape and size of teeth, 

 in the number and distribution, of the spines, etc. It is hardly worth 

 the while to dwell on the characters possessed in common, but rather 

 on those by which we may be able to distinguish the different species. 

 All remarks are to be understood as applying to full grown speci- 

 mens unless otherwise specified. 



The species erinacea and ocellata differ in size ; the former attains 

 a length of from sixteen to twenty inches, the latter, including the 

 variety which is the smaller, varies in length from two to three feet 

 or more. In erinacea the rows of teeth vary from forty-six to fifty- 

 four, in the numerous specimens at hand ; in ocellata the lowest num- 

 ber to be found is eighty, the highest one hundred and ten. The 

 specimens having the lower number are young ones, about the size of 

 the adult of erinacea. For the variety, diaphana, the average num- 

 ber of rows is about ten less than for the species. The claspers in 

 the smaller species when at rest have the hook fitting closely in a 

 crotch of about the same length ; in the larger the hook is some dis- 



