1865.] n. WOODWARD — DUVOKIAN CRUSTACEA. 485 



Thoracic Segments. — The first segment is Ij^^- of an inch in length, 

 and 10 inches in breadth ; the lateral portion is rounded and curved 

 upwards ; the surface is minutely scale-marked. 



The second segment is 17 lines in length, and 10 inches in breadth : 

 a series of long tubercles borders the posterior margin, and the sur- 

 face is covered with minute scale-markings. The lateral portion is 

 rounded and slightly expanded. 



The third segment is 2 inches wide, and 10| broad : three principal 

 prominent tubercles mark the posterior margin, pointing backwards, 

 and also several smaller ones. 



The epimeral portion of all the thoracic segments is widely rounded, 

 and a broad margin of each segment overlaps the succeeding one. 



The fourth segment exposes 1 inch and 10 lines of its length. 



The tubercles upon this and the third segment are the most 

 strongly marked of any. It is 11 inches in breadth. The fifth 

 segment (thoracic) is 1| inch in length, and 9 inches broad. The 

 sixth segment is 19 lines in length, and (about) 8 inches in breadth. 

 The seventh (or first abdominal) is 2 inches in length, and from 

 5 to 6 inches in breadth. (Here the specimen is fractured across, 

 and the margins of this segment are wanting.) Each of the ab- 

 dominal segments has large epimeral pieces, which have been well 

 preserved upon the surface of the overlying slab. 



The eighth (or second abdominal) is 14 lines in length, and 

 5 inches in breadth, including the epimeral portion, which is clearly 

 shown. The ninth (or third abdominal) is 2| inches long, and 

 4| in breadth. The tenth (or fourth abdominal) is 21- inches in 

 length, and 4^ inches broad, including the epimeral portion. The 

 eleventh (or fifth abdominal) is 2^ inches long, and 3 inches 10 

 lines in breadth, including the epimeral portion. The twelfth (or 

 sixth abdominal) is 2\ inches in length, and 3f inches in width. 

 Prom this segment two elongated epimeral pieces are developed, 

 measuring 4| inches in length by about 5 lines in width, and termi- 

 nating in a broad rounded point. 



The telson (9| inches in length) is somewhat broad at the point of 

 attachment, and becomes slightly narrower in the first quarter, gra- 

 dually widening to 1| inch. The central depression is ^ inch in 

 width. The termination is rounded, and the border does not appear 

 to have been ornamented. Of the appendages, there remains only 

 the single joint of a swimming-limb attached to the left margin of 

 the carapace, measuring 4 inches in length by two in breadth, 

 and having a row of tubercles upon the centre. 



In a letter dated 9th February, 1865, Mr. Powrie writes — 



" Mr. Salter has expressed his conviction that Sfylonuriis Poivnei, 

 and ;S'. Scoticus arc specifically the same — the larger one a full-grown 

 male, and the smaller a young female, the longer and narrower body, 

 shorter tail and epimeral appendages being all characteristics of the 

 male ; in other respects the resemblance is most marked." 



But i{ S. Foun-iei and IS. Scoticus be identical, then the determi- 

 nation of the sexes in the British and American species of Eurijpterns, 

 Fterygotus, and Slimonia, by Prof. Hall and myself, is of no avail. 



