360 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxiii. 



the same large raised knobs opposite the second maxilUpeds as in the 

 type species (figs. 20 and 21). 



First pair of dorsal plates widely separated, their posterior margins 

 reaching far l)ehind those of the second pair, and far outside the lateral 

 margins of the third pair. The posterior margins of the first and 

 third pairs of plates are not toothed in any of the specimens at hand. 



Genital segment nmch larger than the carapace, a little wider than 

 long, the width greatest near the center and a little more than that 

 of the carapace. Posterior angles reaching farther back than in the 

 typical form, making the posterior margin more squarely truncated; 

 median sinus narrow and shallow^er than in the type form. Appen- 

 dages exactly like those of the type form except that they are larger. 

 Egg-strings relatively narrower than in the type forni and much 

 longer. 



Ten females belonging to this variety were obtained from a dusky 

 shark, Carcliarliinus ohscurus, at Woods Hole. They are excellently 

 preserved, and are of the same color as the type form, a light yellowish 

 white. They are all fidly developed females with egg-strings, are 

 all exactly alike, and differ from the type in the above particulars, 

 the most noticeable difference being the increase in size and in the 

 length of the egg-strings. 



Rathbun founded his variety on a single specimen which had been 

 in alcohol many years and was of a dark brown color. 



On comparing these fresh specimens with his, they are found to 

 agree in every particular of structure, but are somewhat larger, and 

 are of the same color as the type instead of being browTi. 



This species was established by Rathbun in 1887 upon six lots of 

 specimens obtained from four different hosts. Two additional lots 

 have since been obtained, one of which included the developmental 

 stages and was obtained from a new host. 



The U. S. National Museum collection now includes the following: 

 From the dusky shark, Carcharhinus ohscurus, Cat. No. 12685 from 

 Vineyard Sound, Massachusetts; Cat. No. 8181 from Noank, Con- 

 necticut, and the variety stimpsoni, Cat. No. 4414 and Cat. No. 32775, 

 both from Woods Hole, Massachusetts. 



From the sharp-nosed shark, Scoliodon terrse-novse, Cat. No. 6085, 

 taken at Pensacola, Florida, and Cat. No. 32776 taken at Beaufort, 

 North Carolina. From the blue shark, Carcharhinus milherti, Cat. 

 No. 8180 taken at Woods Hole. From the shovel-head shark, 

 Reniceps tihuro, Cat. No. 8182 taken at St. Marys River, Florida. 

 From the smooth dog-fish, Mustelus canis, Gat. No. 32777 taken at 

 Woods Hole; this lot included the chalimi already described. 



That this is a valid species and not a synonym of Perissopus 

 dentatus, as Bassett-Smith would have us believe, may be seen in the 

 following comparison : 



