MELVILL AND STANDEN : ROSTELLARIA DELICATULA. 163 



Persian Gulf. Gulf of Oman. Latitude 24° 49' N., longtitude 

 55° 56' E., 250 fathoms, mud, all young. Near this sounding six 

 fine examples occurred from 200-400 fathoms. 



Off Jask, latitude 25° 19' N., longitude 58° 10' E., also south of 

 Ras Jazin at 140 fathoms, 7th April, 1903, many adult, with a few 

 Conus {Conorbis) coromandelicus E. A. Smith (previously only found 

 in the bay of Bengal by Messrs. Wood-Mason and Alcock during the 

 " Investigator " Expedition), and a large number of Echinodermata. 



Juvenile examples were rare in shell-sand, which has proved most 

 prolific in new forms of deep-sea mollusca, in the Gulf of Oman. 

 Latitude 24° 58' N., longitude 56° 54' E., 156 fathoms, and, likewise, 

 in March, 1904, it was dredged at 175 fathoms, in some abundance, 

 with Conus coromandelicus in small quantity. 



Off Ras Maidani, at 180 fathoms, it occurred with a few of the rare 

 Pleuroioma navarchus M. & S.^ 



Mekran Coast. Latitude 24° 59' N., longtitude 60° 58' E., 170 

 fathoms, April 8, 1903, all in juvenile state. No other species of 

 mollusc occurred, but many prawns and shrimps came up in the 

 dredge at the same time. 



The mean temperature of the water in the localities affected by this 

 Rostellaria, is, according to Mr. Townsend, 62° Fahrenheit. 



Mr. Townsend having called our attention to some variability in 

 this species, as regards the number of denticles on the outer lip, a 

 close examination of all the examples received from him shews the 

 following result : — 



{a) lip with three processes {tridenticulata). 



(b) ,, four ,, {quatuordenticulata). 



{c) ,, five ,, {(juinquedetiticulaid). 



Of these (/') is the normal form as originally described by Mr. G. 

 Nevill, and the proportion of frequency or the reverse seems to be 

 In (a) I : 75 {l^. 



(c) I : 25 (/.). 



In marking, size, form, and every other particular save that just 

 mentioned, there is a wonderful uniformity in all that we have 

 examined. 



Rostellaria curvirostris Lam. and R. curta Sowb., also occurring 

 in the same seas, are likewise apt to vary somewhat in the number of 

 denticles on the outer lip, normal examples possessing seven in both 

 instances. 



I Ann. &> Mag. Nat. Hist. (7), vol. 12, plate 21, fig. 15, p. 310, 1903. The type, now in the 

 British Museum, is larger and finer than the five or si.K specimens subsequently dredged, but all 

 were alive. All have deep-sea breaks on the body whorl. It is one of the finest of the abyssal 

 forms of Pleufotoma, 



