MOLLUSCA OF THE ' CHALLENGER ' EXPEDITION. 437 



This and P. acanthodes are extremely alike ; but one easily 

 notices the relatively shorter and broader form and the squarer 

 outline and ribbing of this. Under that other I have mentioned a 

 number of features of difference which, though individually minute, 

 concur in marking the distinction of the two species. A compa- 

 rison of this species with P. nuperrima, Tib., = P. decussata, Phil, 

 (not = P. {JEtaphitoma) hispidula, Jan, which is certainly distinct *), 

 suggested by Dr. Grwyn Jeffreys, I was enabled to obtain through 

 the kindness of the Marquis de M onterosato. P. corallina re- 

 sembles that other in the minute blunt prickles which are found 

 on many corals, and which ornament the spirals ; but the ' Chal- 

 lenger' species is far smaller and narrower, the last whorl in 

 particular is very much shorter and less tumid, the whorls are 

 always more angular, the spirals are fewer, the longitudinal ribs 

 are both fewer and stronger, and the apex is utterly different both 

 in form and sculpture. 



37. Pletjeotoma (Mangelia) macra, n. sp. (fiaxpos, long.) 



St. 73. June 30, 1873. Lat. 38° 30' K, long. 31° 14' W. 

 "West of the Azores. 1000 fms. Gloligerina-ooze. Bottom 

 temperature 39 0- 4. 



St. 78. July 10, 1873. Lat. 37° 26' N., long. 25° 13' W. Off 

 San Miguel, Azores. 1000 fms. Globigerina-ooze. 



Shell. — High, narrow, biconical, fragile, translucent white, 

 glossy, feebly ribbed and spiralled, with a stumpy subscalar 

 spire, ending in a large, conical, sculptured, sharp-tipped dome, 

 and with a small body-whorl, contracted base, and produced snout. 

 Sculpture. Longitudinals — there are on the last whorl about 20 

 flexuous oblique threads ; they rise at the suture, retreat very 

 much to the left in the sinus-area, but at the angulation below 

 this they curve round to the right and die out on the base ; the 

 flat intervals which part them are three times their breadth ; the 

 system of longitudinal ribs on the embryonic whorls is very much 

 like that of the shell, but is really different : the lines of growth 

 are very fine, and are quite independent of the ribs. Spirals — 

 below the sinus-area there is a blunt angulation strengthened by 



* The minute ornamentation of the surface in these two species is very 

 similar, and is apt to mislead ; but the form of the whorls and the details, both 

 of longitudinals and spirals, are different The embryonic whorls, too, are dis- 

 tinct, being in P. nuperrirna broader and more pressed down ; the sculpture 

 is diverse also, the longitudinal ribs being the prominent feature in P. nuper- 

 rirna, while in P. hispidula it is the spirals. 



