312 DESCRIPTIONS OF PARASITIC COPEPODA. 



Dorsal appendage of the fourtli segment very laige in proportion to 

 the preceding, and equalling or slightly exceeding the fifth segment in 

 width. It is broadly emarginate posteriorly, or with a short, M'ide 

 sinus, which partly divides it into two well-rounded lobes. The ex- 

 posed i)ortion of the fifth segment is between one-fourth and one-third 

 the length of the entire body, and about one-third broader than long; 

 its greatest width is just back of the appendage of the preceding seg- 

 ment, which is but slightly, if any, wider. It narrows gradually back- 

 ward, the posterior extremities on each side being rather broad and 

 rounded, or in some cases obtusely subangular. The posterior median 

 sinus is large, and regularly rounded at the inner end. 



The caudal plate is small, its free margin forming an arc, equal to 

 about four-fifths the circumference of a comparatively perfect circle, 

 and from one-half to two-thirds its entire length projects back of the 

 posterior lateral extremities of the fifth segment. The caudal stylets 

 are of medium size, and very thick vertically, being thickest toward 

 the outer margin; they narrow gradually, the outer margin being nearly 

 straight and the inner margin slightly curved, or more or less irregular. 

 The width of the stylets near the tip varies somewhat in different 

 specimens; in some cases the stylets taper regularly to a sharp point; 

 in others, the width near the tip is fully half the width at the inner end. 

 They terminate in three stout, pointed spines, arranged vertically and 

 serially, as shown on pi. VI, fig. 2, the lower spine being also the outer- 

 most. A smaller spine projects backward from the lower inner margin,, 

 about one-third or two-fifths the length of the stylet from the tip, and 

 slightly in advance of this spine there is usually a single small seta. 

 The anterolateral angles of the stylets are obtuse, and not produced 

 as in most s[)ecies. In alcoholic preparations, two-thirds or more in 

 length of the stylets are visible from above. The ovigerous tubes are 

 nearly twice the length of the entire body. 



Specimens from the dog-fish and Atwood's shark do not differ much 

 from those above described in the characters of the dorsal surface. 

 The frontal plates are often broader, with a more strongly curved outer 

 margin, in specimens from the dog-fish, while in those from Atwood's 

 shark they are, if anything, a trifle narrower. The posterior margin of 

 the first segment is generally more regular and the si)iues more constant. 

 In the specimens from Atwood's shark the lobes of the second segment 

 are proportionally longer, and that of the third segment is shorter, with 

 a broader mediaw sinus. 



Few of the api)endages of the ventral surface present features that 

 are distinctively characteristic of the species, and as they are all fig- 

 ured on i)lates VI and Vll, but brief mention will be made of them. 



The so-called " sucking disks" of the two anterior pairs, at the bases 

 of the two pairs of antennji?, ar«i rather large, placed near together and 

 in parallel positions; the inner ones are somewhat smaller than the 

 outer, the former being oval, the latter more elliptical, in outline. Thet 



