1873.] MR. R. B.WATSON ON MADEIRAN MOLLUSKS. 379 



into the form and arrangement of the longitudinal bars, which, 

 regardless of the line of the oblique ribs, score the whorls straight 



across. 



- Rissoa similis, Scacchi. (Plate XXXV. figs. 16 & 16 a.) 



Not in M 'Andrew's list, 

 in^f -Selvagens shore; Porto Santo, shore to 50 fathoms; Machico, 



0- 5 fathoms; Santa Cruz, 10-15 fathoms; Piedade (Canical), 

 10-15 fathoms; Ponta de S. Lourenco, 25 fathoms; Porto da Cruz, 

 50 fathoms ; Funchal, 50 fathoms. 



This is a most troublesome species, and would afford any species- 

 monger ample exercise. But on a large collection of specimens it is 

 impossible to establish even well-marked varieties, so variable and 

 interchangeable are the peculiarities of form, sculpture, and colour. 

 Uu the whole, however, there are two distinct varieties-one ribbed 

 the other smooth (var. levis), the former being relatively longer and 

 broader than the other. These varieties are found quite promiscu- 

 ously in ermingled, only that I found the clearest, brightest, and on 

 the whole most aberrant specimens of the var. levis among drift sea- 

 weed on the clean sandy shore of Porto Santo 



Mr. Gwyn Jeffreys (Brit. Conch, vol. iv. p. 37) regards this 

 species as a small variety of R. costulata, to which I would gladly 

 have united it here if I could have convinced myself that that or the 

 others of that unsatisfactory group had anv better right than this 

 species of Scacchi to separate recognition. In their present hopeless 

 state I prefer to leave them alone. ' 



7 «^ Rissoa albugo, Watson. (Plate XXXV. fig. 1 7.) 



' thf k£ Eftf l0 , n °'.P eculiar as b f in S lightly spindle-shaped, from 

 17 h , alf .7 h " rl bein S contracted in its breadth and drain out in 

 length glassily transparent, thin, smooth, and glossy. 



Sculpture One distinct but very fine and shallow spiral furrow 

 like a scratch, shows itself just below the periphery but above corner 

 of lip, and runs round to very edge of lip in front ; below this the 

 whole base is covered with a series of very faint equally dLtanced 

 spiral lines about -^ inch apart, very rarely" visible ; above per Tery 

 a senes of stdl fainter and more minute spiral lines can sometimes be 

 seen, as it were, in the substance of the shell : the whole surface is 

 covered with very faint, flexuous, longitudinal lines of gowth these 

 alone are traceable on upper whorls. 



Colour when fresh, transparent glassy white, with a yellowish 

 tinge, dotted with minute, ^-inch square, crimson, angukr dots 

 arranged in series of spirals 10 to 20 in number, about as numero us 

 above the spiral furrow as below it ; these are sometimes aTat d 



s uar:t re S la o' t w ei ' ValS - in the T'T™ Spirds M t0 f °™ P^S 

 squares in other specimens they become, above the peripherv 

 ongi udina ly confluent in pairs so as to form couple S P of l£fe 

 longitudinal crimson lines (about twelve couples on lasfwhorl fewer 

 on preceding) somewhat irregular, interrupted, and flexuous Zl 

 pair are parted from the next set by a space somewhat broader than 



