KONGL. SV. VET. AKADEMIENS HANDL. BAND. 19. N:o 6. 49 



as belonging to his Chiton? cordatus^). It may now be questioned whether all these 

 similar fossils truly be reruains of Chitons or not. What most strongly militated against 

 their belonging to that fainily of Gastropoda was the circumstance that they are all 

 entirely wanting the characteristic two apophyses or sutural laminaj which are si- 

 tuated in the anterior margin of the plate and believed to be present in all recenl 

 Chitons and in almost all the palajozoic ones described by de Koninck, Ryckholt, 

 KiRKBY, BAir.Y, Salter and Sandberger. In the Gotland specimcns and, as far as one 

 is able to judge from the figures and descriptions of Barrande and Kirkby, also in the 

 Bohemian and the supposed median plates of Chiton? cordatiis there is not the least 

 trace of there ever having been any apophyses. Nor does the elongate shape of the 

 plates, generally longer than broad or often of the same height as breadth, agree with 

 the transverse form of the plates so common amongst the recent and fossil Chitons. 

 As Kirkby remarks (Qu. Journ. Geol. Soc. vol. 15 p. 617) there is, however, one of 

 the recent Chitons, Ch. hastatus Sow. ^), in whieh the interniediate plates bear a close 

 resemblance to the palteozoic ones. Moreover, in tlie recent genus Leptochiton Car- 

 penter, now confined to the arctic and temperate seas, there is an approach to the 

 plates in the palaaozoic Chitonidaa as they are without any laminaj of insertion, but 

 raostly provided with sutural larainaj^). 



On the inside of the plates of Chelodes there is also a feature, which is by far 

 not so prominent in Chiton. At the pointed posterior end of the inside is a large 

 triangulär area, covered by transverse, parallel, curved lines of growth. In Chelodes Berg- 

 mani, for instance, it occupies a little more than half the length of the plate. A similar, 

 I should be inclined to say a homologous, area is seen ou quite the corresponding 

 place in the more recent Chitons, although it there in raost of the transverse plates is 

 restricted to a narrow stripe. In others again it occui)ies nearly a third of the total 

 length of the plate. It seems hardly to have receivcd all the attention it deserves, 

 even not by such an accurate monographist as Middendorff. It is evidently with this 

 part of the interiör surface that the plates posteriorly overlap each other and which 

 consequently is not covered by the tissues of the animal. By the continued growth of 

 the plate this area must be enlarged, when the soft tissues retire and a new line of 

 growth is added to it. The mode of formation of the interiör apical area of Chelodes 

 has in all probability been the same, although it is enormously more developed than 

 in most Chitons, perhaps only having its counterpart in Chit. hnstatus. 



Excepting the Chitons there are no other shell-covered animals with which Che- 

 lodes may be compared than the Lepadida;. Amongst the numerous valves, which 

 form the integument of the Lepadida^ there are only two or three regularly formed, 

 whilst all the others are more or less oblique. There is indeed some similarity be- 



') »On the permiaii Chitoiiidix;". Qn. Journ. Geol. Soc. vol. 15 (1859) p. 61G, pl. IG (igs. 25 — 26 and 

 also in the Geological Magazine vol. 4, p. 341, pl. 16 ligs Ila — 11b, whero Kiukby and .T. Young describe 

 the Chitons from the Garboniferovis strata of Yorkshire and Western Seotland. 



^) Reevr Coiichologia Iconica, vol. IV. pl. 25 fig. 166 and plate showing details of sculptiiro, enlarged 

 fig. 166. 



■') Dali,, H. W., the resnlts of the recent investigations into the Natiiral Hist, of the (Miitonidae. Sraith- 

 sonian Miscellaneous Collection, vol. XX, p. 193. 



K. St. Vot.-Ak.ad. Haiidl. Bd. Ii). N:o C. 7 



