KONGL. SV. VET. AKADEMIENS HANDL. HAND. 19. N:0 6. 65 



densely set, as it were, in groups of two or three with smooth interstices. They are 

 wavy or interrupted in their continuity by the transverse lines. As is seen on pi. II 

 f. 36, they form minute, steplike gradations or, as it were, terraces, each of the upper- 

 most ones lying a little higher, than the succeeding inferior. The transverse lines form 

 a sigmoid bend when they, more or less crowded, more or less prominent, continue 

 from the suture to the umbilical side. The coarser ones which in most instances re- 

 present the outlines of former apertural lips are wavy or notched by two or three 

 angular slits. On the spire they end towards the suture as a thin and sharp lamina, 

 which bridges over the suture to the next whorl. 



The spire is short in the most common variety, depressed and, as stated, even sunk 

 in specimens which are planorbiform. The whorls vary in number from three and a 

 half to four and a half. Tiie last one is sometimes so much enlarged and widened, 

 that it surpasses the spire with the lower rim of the aperture. The suture is tolerably 

 deep. 



There is a tendency in the body whorl to grow out free, without any connection 

 with the older whorls, as is manifested in several specimens delineated on plate II. In fig. 

 48 it is just beginning to free itself, in figs. 50, 51 it is disconnected for a longer distance 

 and tubular and in figs. 47 & 49 the whorls are nearly uncoiled. This is an approach to what 

 is permanent in the younger Devonian and Carboniferous species and also in the Silurian 

 Orthonychi*. This peculiarity in the formation of the shell is what the German authors 

 call MSkalaridenbildungi), and may be found amongst several recent shells, where the 

 last whorl as in Vermetus is free and tubular. Scalarid shells live together with nor- 

 maly coiled of the same species, and races, varieties or even new species may take their 

 origin from them if they prevail and persist. Thus resembling forms of analogous 

 formation may arise or be repeated in genera which are not in the least related. 



The aperture is oval, oblique or transverse, its margins thin or thickened, the 

 columellar lip reflexed or in some specimens only in a small degree hiding the umbi- 

 lical fissure. Sometimes it is so much developed that it completely covers the umbi- 

 licus, and thins out against the whorl, pi. II fig. 29. In some this lip, pi. II f. 37, 

 38, is thick and twisted and shows thus the characters of the genus Strophostylus. 

 The exterior lip is regularly bent, sinuose or lobate. In pi. II fig. 32 and still more 

 so in pi. Ill fig. 6 there are instances given of a highly sinuose aperture. In fig. 6 it 

 is wrinkled and bent in several creases and folds. This is probably owing to the 

 circumstance that they have been fixed to the shelly surface of soine other marine 

 animal and long time enough to have moulded the aperture according to the sculpture 

 of this substratum. As is the case with the I'.nglish and American specimens of this 

 species and also with Platj'cerata from the Carboniferous formation of North America, 

 these shells are sometimes found fixed on the pcrisome of Crinoids, as for inst. on Perie- 

 chocrinus. When such sinuosities occur in the oiiter lip there is formed on the median 

 line of the body whorl what in a distant manner reminds of the slit I)and of the Pleuro- 

 tomaria;. It consists of the wavy lines of growth on the former site of a sinus. In 

 others, as in the specimen which is the original type of Hisinger's Acroculia sulcata 



K. Vet. Akail. Ilnnrtl. P.,iii(l Ifi N:o il 9 



