:24 JOHAN KLEH. [SEC. ARCT. EXP. FRAM 



i ' u t er Characteristics. The plate is quite ilat; length 

 !> mm., breadth \~> nun. and thickness \Jt mm. Only the upper sur- 

 face i- visible: it shines brightly like black enamel, and the sculpture is 

 very beautiful and characteristic. (PI. II, lig. ^; PI. Ill, figs 12). By 

 the naked eye it appears to be finely and regularly tnbercnlalrd as is 

 the case with many coccosteomorph (ishes. hnl even a slight enlargement 

 >lmws that ihe sculpture is markedly psammosteid. 



The latter is composed of fairly regular rows with markedly ribbed 

 denticles, the points of which do not lie in the centre, but are quite 

 peripheral to the longitudinal direction of the rows. The highly gliste- 

 ning denticles for this reason when slightly magnified have a unique 

 arrow-like form, which however is less striking under higher power. 

 \\V then observe that the denticles have fine, sharp, and to some extent 

 crenulaled rib-, which all run towards the peripherally situated point. 



'Jlie length of the denticles is 0.7 0.9 mm.; the breadth is the same. 

 No\\ and then we see quite small ones. The spaces between the former 

 are seldom wholly extended: here and- there, however, we notice that 

 thev run almost directly towards one another. 



mi 



Interior Structure. Microscopic examination shows that the 

 structure is markedly psammosteid. (PI. Ill, fig. 3). The denticles are 

 closely .situated, but between them open spaces without skeleton sub- 

 stance are clearly visible. The pulp cavities are very wide and open 

 downwards with wide orifices, communicating in this manner with the 

 underlying vascular canals. The latter are narrow and irregular above, 

 with thick walls that as is usually the case show a lamellar structure 

 without bone cells, heeper down the canals and lacuns become wider 

 and more regular, with thinner walls. Underneath there are again 

 traces df narrower canals which render probable the original existence 

 "f a basal layer. The plate, however, is incomplete at this point. 

 Farthest to the right, bevond the part of the microscopical section shown 

 in Ihe illustration, (a transversal .section), the somewhat close network 

 grows larger and larger, until at length it occupies Ihe whole thickno- 

 ol the plate, which at this point becomes thinner. \Ve may therefore 

 presume that at this point there has been a free margin. Between the 

 denticles the canal svstein opens upwards in pores. 



2. Another quite small fragment (S. I. M a) is shown in PI. II fig. 1, 

 " limes enlarged. The denticles are here greatly extended; as however 

 the strong rib-, ih,. peripheral points and the large pulp cavities agiv.- 



in all respects with those of L. above specimen, there can be loubt 



that they belong to one and the same form. 



