468 MARINE BIOLOGY OF THE SUDANESE RED SEA. 
1900 by Alcock for four specimens from Aden and the Baluchistan coast, 
is a synonym of this species. 
The characters by which Alcock separates his species from D. sulcata are : 
(1) the absence of the spine from the under surface of the arm; (2) the 
presence of a tympanum on the dorsal surface of the merus of the last pair 
of walking-legs, and (3) the fact that the fingers are shorter than the palm. 
The condition of each of these characters in my specimens is shown in the 
following table :— 
No. of Shee. Cl. H.1. (upper | 777, Hil. Meral 
specimen. bord.). Jal, spine. Tyop ann) 
mm, mm. /mm. 
401. 2 56 11955 3:0 2-00 Absent. [Leg lost. ] 
402. e 59 15 30 2-00 Absent. Present. 
403. 2 6:0 15 3:0 2:00 Absent. Present. 
404, 2 6°5 16 35 2:19 Absent. [ Leg lost. } 
Average in 
40s =2°05. Absent Present 
in all. in both. 
299. S 50 20 |30| 180 | Absent. | Present. 
398. 3 59 19 34 1:79 Absent. | Absent. 
394. 3 6:0 2°] BY) 152 Absent. Absent Rt. 
| [Left lost. | 
395. of 6-0 2-0 Be 1-75 Absent. Trace. 
396. 3 6:0 2-0 32 1:60 Absent. Present. 
397. ef 6:0 2°05 Bu 1:48 Absent. Present. 
398. i Gon 2° 3:8 1-52 Absent. Present. 
399. re 7:0 | 2'8 3:9 | 1°39 Trace. Present. 
400. & | 30 42 1:40 Present. Present. 
Average in 
9 gs =1:55. | Absent7. } | Present 6. 
| Trace 1. | Trace 1. 
| Present 1.) | Absent 2. { 
It will be noted from the above table that the most usual condition is for 
the spine to be absent and the tympanum present, this occurring in six 
instances (seven if 395 be included); but in one specimen (two if 399 be 
included) both spine and tympanum are present, and in two specimens bel 
are absent. This agrees with Nobili’s results. 
The remaining point of difference, namely, the relative size of hand and 
