188 LEPTOTHYRA. 



supporting wings. Laterals narrow, with simple cusps and supporting 

 wings, the outer narrower and with bidentate cusp. Inner marginals 

 with very large cusps. (See Troschel.) 



Genus Leptothyra. 



I have examined the dentition of the following species : L. car- 

 penteri, (pi. 60, fig. 73,) L. bacii/a, L. kcia, L. aviussittata, L. sangaren- 

 sis, (pi. 61, fig. 15) L. granulosa. In all of these species the median 

 teeth are oval, wide, with a narrow projection above, and more or 

 less narrowed toward the base ; the u]>per margin is in no case re- 

 flected, so that cusp, cutting point or edge, in any usual sense, there is 

 none. In L. carpenter'i and L. hacula, however, there is a ledge or 

 thickening, more or less irregular on its lower raai'gin, extending 

 across the body near its upper margin ; but this is not formed by a re- 

 flection of that margin, and so cannot be considered as a cusp ; in the 

 other species this structure is absent. The lateral margins are pro- 

 duced into supporting wings. The laterals are long, excavated on 

 the inner side for the reception of the supporting wings of the cen- 

 trals, and with a process, b, underlying these supporting wings. 

 Their outer margins are produced into supporting wings like those 

 of the centrals. The cusps are provided wdth several minute denti- 

 cles at their outer bases. All of the laterals are of this form, except 

 the outer ones which have no supporting wings. The marginals are 

 armed with long blunt narrow cusps, which are longest on the teeth 

 about the sixth from the inside, and decrease in size in either direc- 

 tion from that point ; about the twelfth from the inside their margins 

 begin to become serrate. It will be seen that my results are very 

 different from those obtained by Troschel, who has figured the rad- 

 ula of /j. carpenteri (under the name of "L. coccineus Desh."). I am 

 constrained to believe that, owing probably to some imperfection in 

 his preparation or other cause, he misinterpreted certain structures 

 of these minute radulje. The characters of the radula lend no sup- 

 port to the opinion expressed by some authors as to the position of 

 this genus in the Trochidce ; but it is not very closely allied to any 

 group- of the Turbinida'. I am undecided about the nature of the 

 projection from the upper margin of the central tooth of Leptothyra ; 

 it may be homologous with the basal plate of the j)receding groups ; 

 but if so it seems to be united with the body as far as the upper 

 margin of the latter, — a condition which is not found in Turbo, etc. 



In concluding this review, I wish to direct the attention of con- 

 chologists to the desirability of procuring and examining the radula; 



