94 OPISTHOBRANCHIATA OF BRAZIL 



According to the descriptions and figures of Trinchese Cy8) 

 the single crest is found upon the fulcrum of the right mandible, 

 the double crest upon the left one in Spurilla neapolitana, which 

 is the reverse of the condition here described. In the preparations 

 which I have made of the mandibles of Sp. neapolitana the rela- 

 tions of the single and double crests is the same as that which I 

 have found in Sp. hrasiliana. I am at a loss to explain the con- 

 tradiction in results. 



Radula. The radula is uniserial, consisting of a series of 

 eighteen strongly arched slightly emarginate pectinate plates 

 of an amber color. These plates increase rapidly and regularly 

 in size from before backward, and present a slightly convex ante- 

 rior face. The first five plates have their central denticles worn 

 and broken, the last five are still inclosed in the radula sheath 

 where they are developed. The dimensions of the individual 

 teeth range from a basal width of 0.27 mm., and a height, meas- 

 ured from the middle of the base line to the top of the middle 

 denticle, of 0.225 mm., in the first plate, to a width of 0.425 mm., 

 and a height of 0.30 mm. in the eighteenth plate. The relative 

 proportions are well shown in PI. XVI, figs. 83 and 84, which 

 illustrate the twelfth and the first plates of the radula respectively. 



Each plate is slightly emarginate at its summit (PI. XVI, fig. 

 89), but none so much so as to give the bilobed appearance 

 figured by Bergh ('64, '71), Trinchese ('78) and Vayssiere ('88, 

 '03) for the other species of this genus. The denticles are slender 

 and lanceolate, the lateral ones slightly curved, the remainder 

 straight, increasing in length from the sides upward, and reaching 

 a maximum height about the eighth or tenth from the center. The 

 central denticle is low and broad, usually with a small denticle 

 next to it on either side, the succeeding ones increasing 

 in length rapidly. The number of denticles in the first plate is 

 49:1:49; in the fifth 39:1:40; in the twelfth 57:1:53; in the 

 fifteenth 61 :i :63; and in the eighteenth 49:1 :47, the increase in 

 number thus being irregular. In a radula taken from an indi- 

 vidual of Sp. neapolitana of the same body dimensions this in- 

 crease in the number of denticles is much more regular, repre- 

 sentative plates running as follows. First plate 18:1:15; fifth 

 plate 23 :i : 23 ; tenth plate 34 :i : 34 ; twelfth plate 32 :i : 35 ; fifteenth 

 plate 35 :i : 37; eighteenth plate 52 :i : 44; and in the twenty-sixth 



