KONGL. SV. VET. AKADEMIENS HANDL. BAND. 19. N:0 6. 49 



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

 siinihir fossils truly be remains of Chitons or not. What most strongly militated against 

 tlieir belonging to that family of Gastropoda was the circumstance that they are all 

 entirely wanting the characteristic two apopliyses or sutural lamina) which are si- 

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

 Chitons and in almost all the palaeozoic ones described by de Koninck, Ryckuolt, 

 KiRKBY, Baii.y, Salter and Sandbergek. In the Gotland specimens 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? cordatus 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 thi; plates so common amongst the recent and fossil Chitons. 

 As Kirkby remarks ((^u. Journ. Geol. Soc. vol. 15 j). G17) there is, however, one of 

 the recent Chitons, Ch. hastatus Sow."), in which the interniediate plates bear a close 

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

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

 plates in the palaeozoic Chitonid;c as they are without any laminae of insertion, but 

 mostly provided with sutural laminae'). 



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 

 triangular 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 on quite the corresponding 

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

 restricted to a narrow stripe. In others again it occupies nearly a third of the total 

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

 even not by such an accurate monogra[)hist as Middendorff. It is evidently with this 

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

 consequently is not covered by the tissues of the aniiruil. By the contiinu'd growth of 

 the plate this area must be enlarged, wlien the soft tissues i-etire and a new line of 

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

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

 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 Lepadidae. Amongst the numerous valves, which 

 form the integument of the Lepadidae 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 pcrmian ChitoiiidiXi". Qn. .Joiirn. Gcol. Soc. vol. 15 (1859) p. G16, pi. 1(5 i\s:s. 25—26 and 

 also in flic Geological Magazine vol. 4, p. .'Ml, pi. 16 figs 11a — lib, where KntKBY and J. VonNG describe 

 the Chitons from iho Carboniferons strata of Yorkshire and Western Scotland. 



'-) Rkf.vr Coiicholngia Icoiiica, vol. IV. pi. 25 fig. 166 and plate showing details of sculpture, enlarged 

 fig. 166. 



•*) ])AI,t,, II. W., the results of the recent investiijations into the Natural Hist, of the ('hitonid;*^. Smith- 

 sonian Miseellaneous Collection, vol. X.\, p. 193. 



K. Sv. Vct.-Aknrt. naiuU. Hil. 10. N:n li. 7 



