Crustacean of the Genus Mysis. 431 



Mysis Spiritus, n. s. PI. VIII. figs. 1 & 1*. 



Mysis gracilis, pellucidus, vitreus. Thorax cylindricus. Abdomen 

 a thorace ad caudam gradatim diminuens ; abdominis segmentum 

 penultimum longius quam caetera. Appendix antennarum squa- 

 miformis subtriangularis, apice acuto ; spina in medio marginis 

 exterioris posita; margo interior atque exterior supra spinam 

 dense ciliati; margo exterior sub spina non ciliatus. Thoracis 

 frons vix rostrata, fere subtruncata. Pedunculi oculorum longi, 

 appendicisque antennarum dimidium superantes. Antennae breves, 

 thorace vix longiores. Telson apice fisso intermedias fere sequat 

 lamellas ; fissura brevis. 



A perfectly colourless, glassy, transparent species, and, like 

 M . Oberon, scarcely to be distinguished except by its black eyes ; 

 very slender and graceful in form. Carapace cylindrical, not 

 widening behind. Abdomen gradually tapering towards the 

 tail. The front margin of the carapace can scarcely be said to 

 be rostrate, being very nearly truncate. Antennal scale sub- 

 triangular, with the apex acute, not twice as long as the very 

 long peduncle of the eye, and slightly exceeding the peduncle of 

 the interior antennae; a spine placed half-way up the outer 

 margin ; internal and external margins above the spine densely 

 ciliated ; external margin below the spine plain. Antennae re- 

 markably short, not so long as the carapace ; the peduncles of 

 the interior exceed their filaments in length. Telson two-thirds 

 the length of the intermediate lamellse ; the bifurcation is through 

 about a third of its length. 



Taken in sandy rock-pools at the " Black Hall Rocks," on the 

 coast of Durham. 



The following differential characters may be usefully borne in 

 mind by the carcinologist : — 



M. Lamornce has no spine on the antennal scale. 



M. fiexuosus has a spine at the apex of- a lanceolate, obliquely 

 truncate scale. 



M. Spiritus has a spine about the centre of the outer margin 

 of a subtriangular pointed scale. 



EXPLANATION OF PLATE VIII. 



Fig. 1. Mysis Spiritus (Norman). [The spine on the antennal scale is 



represented too high up.] 

 Fig. 1*. Telson of Mysis Spiritus. 

 Fig. 2. Head of Mysis fiexuosus (Muller). 

 Fig. 3. Tail of the same. 

 Fig. 4. Head of Mysis Lamornce (Couch). 

 Fig. 5. Tail of the same. 



Sedgefield, co. Durham, Oct. 22, 1860. 



