52 





migt nedad bøiede Eger eller Straaler, hvilke alle støde 

 sammen i et cirkelrundt og noget convext Nav eller Umbo, 

 som ligger dybere end Ringen, saa at Hjulets øverste 

 Flade er lidt udhulet og har Formen af en ganske lav 

 Kop. Yngre Hjul (Fig. 15, 16), der ere omtrent halvt saa 

 store som de ældre, have sædvanlig færre og noget bre- 

 dere Straaler end de ældre (Fig, 17), men ofte ligesaa 

 mange Tænder som disse. Man vil af ovenstaaende Be- 

 skrivelse se, at Kalkhjulene hos nærværende Form have 

 den største Lighed med samme af Myriotrochus Rinkii 

 Steenstrup (Videnskabelige Meddelelser fra den naturhist. 

 Forening i Kjøbenhavn 1851, Tab. 3, üg. S), navnlig ved 

 deres talrige Straaler og Ringens Besætning med stærke 

 Tænder, hvorved de adskille sig fra de lignende Dannelser 

 hos Chirodota, hvilke altid kun have 6 Straaler og mangle 

 de stærke Tænder paa Ringen. Den eneste Afvigelse, de 

 vise, bestaar deri, at de i Regelen have et ringere Antal 

 af Straaler end hos Myriotrochus, og at disse i Antal ikke 

 svare til Ringens Stykker eller Tænder, medens disses An- 

 tal stemmer overens med det for Myriotrochus normale. 

 Som Exempler herpaa og paa Variationen i Antallet af 

 baade Straaler og Tænder anføres her Antallet af disse 

 Dele hos 10 forskjellige Hjul: 



Kalkhjul. 



No. 



1.. 



2.. 

 3.. 

 4.. 

 5.. 

 6.. 

 7.. 

 8.. 

 9.. 

 10.. 



Antal af Straaler. 



11 

 10 

 13 

 12 

 13 

 12 

 14 

 16 

 13 

 11 



Antal af Ringens Stykker og Tænder 



19. 

 23. 

 17. 

 21. 

 21. 

 24. 

 23. 

 19. 

 24. 

 22. 



Hos Myriotrochus Rinkii svare derimod Straaleme nøi- 

 agtigt til og alternere med Ringens Stykker og disses 

 Tænder. 



En væsentlig Forskjel mellem vor Oligotrochus og 

 Myriotrochus bestaar deri, at Hjulene hos den første ligge 

 indsænkede i Huden, medens de hos Myriotrochus rage 

 frit frem over Hudens Overflade, baarne paa Hudstilke; 

 endvidere deres Forekomst alene nær ved begge Ender af 

 Kroppen samt deres yderst ringe Antal, medens hos Myrio- 

 chus Kroppens hele Overflade er saaledes „oversaaet med 

 Kalkhjul, at der paa hver Qvadratmillimeter af Rygfladen 

 kan regnes 9 Kalkhjul, og paa Bugfladen, hvor de staa 

 mere spredte, 3". Det bemærkes sluttelig, at Hjulene hos 

 vort Dyr ere af betydeligt ringere Størrelse end hos Myrio- 

 trochus Rinkii. 



Tarmkanalen, (Fig. 1 og 2, dd) der sædvanlig er fuld- 

 stoppet af Dynd og derfor skinner brunsort igjennem de 



strong tooth turned inward; and of a likewise variable 

 number (10 — 16) of cylindrical smooth spokes or rays very 

 slightly curved downwards, all meeting together in a circu- 

 lar and somewhat convex nave or umbo which lies deeper 

 than the ring; so that the upper surface of the wheel 

 is a little hollowed and has the form of a quite shallow 

 cup. Younger wheels (fig. 15 — 16) which are about half 

 as large as the older ones, have usually fewer and some- 

 what broader spokes (fig. 17), but frequently not fewer 

 teeth than the older wheels. It will be evident from the 

 above description that the calcareous wheels in the pre- 

 sent form have the greatest resemblance to those of My- 

 riotrochus Rinkii Stenstrup (Videnskabelige Meddelelser 

 fra den natnrhist. Forening i Kjøbenhavn 1851 Tab. 3, 

 üg 8) especially in their numerous radii and in the strong 

 teeth situated on the ring whereby they distinguish them- 

 selves from similar formations in the Chirodata, which 

 have always only 6 radii and are destitute of the strong 

 teeth on the ring. The only difference noticeable consists 

 in the wheels having a smaller number of rays than in the 

 genus Myriotrochus; and the rays not corresponding in 

 number to the pieces or teeth of the ring, while the num- 

 ber of these latter is always the same as the normal num- 

 ber in the Myriotrochus. In illustration of this and of the 

 variation in the numbers of both radii and teeth, the num- 

 bers of these parts in 10 different wheels are here noted. 



Number of radii. | Number .of pieces and teeth 

 | m the ring-. 



No. 



1. 



2, 

 8. 

 4. 



5. 



7. 



8. 



9. 



10. 



11 

 10 

 13 

 12 

 13 

 12 

 14 

 16 

 13 

 11 



19. 

 23. 

 17. 

 21. 

 21. 

 24. 

 23. 

 19. 

 24. 

 22. 



In the Myriotrochus Rinkii the radii correspond exactly and 

 alternate with the pieces of the ring and their teeth. 



One essential difference between our Oligotrochus and 

 the Myriotrochus consists in the wheels in the former lying 

 sunk in the skin; while those of the Myriotrochus project 

 freely over the surface of the skin, being supported on 

 skin-stalks. Another difference appears in the ex- 

 tremely small number of the wheels, and their occurrence 

 only near to the extremities of the body, while the whole 

 surface of the body in the Myriotrochus is so "overstrewn 

 "with calcareous wheels' that on every square millimetre 

 "of the surface of the back, 9 calcareous wheels may be 

 "counted, and on the ventral surface, where they are more 

 "dispersed, 3". Lastly it must be remarked, that the wheels 

 in our animal are of considerably smaller size than in the 

 Myriotrochus Rinkii. 



The intestinal canal (fig. 1 and 2, dd.) which is usually 

 full of mire, and therefore appears brownish black through 





