ISOPODS OF NORTH AMERICA. 



459 



"The body is robust, the length but little exceeding twice the 

 breadth. The head is broad and produced in the median line into a 

 prominent, acute spine, or rostrum, about as long as the head. The 

 antero-lateral angles are also produced and very acute, but do not 

 extend as far as the rostrum. The eyes are rounded, semi-oval, with 

 the long axes converging toward a point near the base of the rostrum. 

 The basal segment of the antennulse is less than one-third the length 

 of the rostrum. The second segment is about as long as the first, but 

 of only about half its diameter. The flagellum equals, or slightly sur- 

 passes, the third antennal segment, and consists of about twelve seg- 

 ments. The scale or spine on the second segment of the antennae is 

 slender and considerably surpasses the third segment. The external 

 lamella of the maxillipeds has the 

 outer angle prominent, though not 

 acute. 



"The thoracic segments are pro- 

 duced laterally into one or two acute 

 angulations, giving a sharply ser- 

 rated or dentated outline to the tho- 

 racic region. The first segment is 

 shorter than the second; the sec- 

 ond, third, and fourth are about 

 equal in length ; the fifth is about the 

 length of the first; the sixth and 

 seventh each a little longer. The 

 first segment is acutely produced at 

 the sides, around the sides of the 

 head, and bears, near the middle 

 of the anterior margin, two short 

 spines, situated about half as far 

 apart as are the eyes, and directed 

 upward and somewhat forward. 

 The second segment has both lateral 

 angles produced into triangular, 

 acute processes, of which the anterior is more slender than the poste- 

 rior and directed more strongly forward. The dorsal spines on this 

 segment are a little farther apart and larger than in the first segment. 

 In the third segment the lateral angulations are more nearty equal 

 than in the second segment and directed less strongty forward. In 

 the specimen figured the third segment bears, on the left side, a 

 single broad angulation, apparently representing the posterior, while 

 the anterior is only indicated by a slight irregularity in the outline. 



"Malformations of this kind appear to be common. The dorsal 

 spines on the third segment are much as in the second. On the fourth 

 segment the anterior angulation is longer than the posterior, and both 

 are directed nearly outward. The dorsal spines on the fourth segment 



FIG. 515. lOLELLA SPINOSA (AFTER HAR- 

 GER). X G. 



