!'A. 

 1 



oil tlit- dorsal part of the apertural expansion. Tlio inner side of the aperture is 

 always smooth. 



.inlin^ tin- expanded aperture, we believe that it was developed only once 

 luring the life of the animal, and that it marks the fully matured condition. Two 



ba lead us to this opinion: first, the uniform size (in each species) of the speci- 

 men* in \\ Inch it is developed or preserved; and second, the thickness, as of age, to 

 which the cxpati'lfl rim may attain. As demonstrating the first we will give the 

 result- nf measurements of two species. In ten average specimens of S. riclun<m<l- 

 the hi^'ht of the shell, excluding the apertural expansion, is 45 mm. in the 

 smallest and only 50 mm. in the largest: in live specimens of S. buelli the same 

 measurement varied between 35 and 37 mm. Herein lies the principal difference 

 between N<i//>im/w/<>w and Tremanotus, and it at the same time explains the 

 'Ifvelojmifiit of a row nf small openings in the latter instead of a single long slit 



In Ti-rintinnfuti, namely, the expanded aperture is a periodic development, a new 

 one being formed at frequent intervals. There is, therefore, no narrow limit to the 

 size of the specimen. The expansion is also always very thin, and the old ones were 

 either broken away or reabsorbed, the latter being in our opinion more likely. As 

 in Suljtini/ost'itH'i. the development of each expansion was preceded or accompanied 

 by the anterior closing of the apertural slit, continued growth at last producing a 

 row of openings instead of a continuous fissure. The number of these openings 

 remaining uncovered varied probably according to their sizes and with the species. 

 The only evidence on this point now available is furnished by casts of the interior. 

 These seemed to show that they remained open for a distance equalling about a 

 third of a volution. In this distance, which slightly exceeds the average length of 

 the slit in S<ili>in>j(ix(r>ni>i, different species of Tremanotus show from four to about 

 ten openings. 



The surface markings of Tremanotus longitudinalis Lindstrom, the only species 

 of tin- gpmis on which they have been observed in a thoroughly satisfactory manner, 

 are on the whole more like those of Bucania than tialpingostoma, but as they are 

 1'r.K-tirally of the same type in all three genera, they are of but little assistance in 

 referring a shell to its proper genus.* 



Finally, we wish to state emphatically our conviction that Buamm, Sa/pinyos- 

 and Trtmanotus stand in close generic relationship to each other. The 



K..krn draw* KMM IB* dUtlootloa* between the different urf < viilpturlnxi of number of European and OM 

 Arlpn 'peclw belonflnc In tfaU connection. jv If hi* oter*aUoM on UM otben arv 



HUM which prrtaln o TiimmuMf. they are certainly of Irule value. But w. art pertaap* more Mvera here than 

 Hoe* ! oar opinion Dr. KokcD ha* (Ire* uanoM pral worth j od valuable work. B-aii*e of Iheceneral minute**** 

 and oorrwtn-*. of his obMrnUtoM. aa error *o palpable u the OM be ha. fallen Into with iMpKt to Tnma* 

 r T rriid nor* than coodeanwd. Where he (ol tbe Idea Ibat the InMrWd* of the aperture In TrmoMfeu I. radially 

 awl thai "the told* are rmtrloMd to UM Inner .td tad In no wUe dependent upon the outer .1 . >nd our coapM- 



Mln. It to (Imply not a fact. 



