KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 25. NtO 2. 



73 



In most species of Calceocrinus and Halysiocrinus, however, the specialisation of the 

 arms has proceeded to such an extent that this presentment of the law is more philoso- 

 phical than praetical. The conspicnous feature of these genera is, as just stated, the series 

 of eontiguous axillaries formed by the ossieles on the extreme left of the arm. These 

 may be called the main-axils», and the whole braneh given off from the right (abanal) 

 or, as it is often termed. the upper slope of each main-axil, may be called an axil-arm. 

 The main-axils are, of course, the primaxil, left secundaxil, left tertiaxil, and so on; it 

 will therefore be natural to eall the arms primaxil-arm, secundaxil-arin, tertiaxil-arm, 

 and so on. Now it is obviously convenient to treat each axil-arm as a separate unit; 

 we need then to formulate our law with reference, not to the whole arm, but to its con- 

 stituent axil-arms. This may be done without reference to specimens if we remember 

 that each succeeding axil-arm starts one higfaer in the brachial series than the one pre- 

 ceding it. An v mere re-setting of the law in this manner would, however, be cumbrous: 

 a shorter method must be devised. Since we cannot apply the terms primibrach, secundi- 

 brach &c, to the series in each of the axil arms themselves, it will be best to call them 

 bv Greek letters, — Alphabrach, Betabrach and so on. Thus Ilax abr. would mean the 

 first series in the secundaxil-arm, I Vax yhw would mean the third series in the quart- 

 axil-arm, and so on. The law may then be most simply stated as follows: — simple 

 armlets are given off from the right side of the ce, y, s axillaries (odd numbers), and 

 from the left-side of /?, <)', C axillaries (even numbers). To afford a concrete instance and 

 at the same time a proof of the truth of this law, the following table has been con- 

 structed from the two best specimens of Calceocrinus gotlandicus. In this table the num- 

 bers of ossieles in each braneh or series are set down; the armlets are denoted by the 

 sign +, which may also be taken to mean that probably more ossieles existed than can 

 be seen in these specimens; the series of the arm, from which the armlets are given off, 

 are denoted by »ax»; when more than one number is given, there is a difterence between 

 the two specimens; the sign x stånds as usual for an unknown quantity. The iteins in 

 broad-faced type represent the thicker portions of the arm, as explained on p. 74. 





Table of Ann-ossicles 



in the Ante] 



•ior 



Ann of Calceocrinu. 



3 gotlandicus. 





n 



— 



— 



— 





— 



•r + 



•rax 



n 



^j 



L 



— 



— 



./•ax 



x + 



— 





3ax 5 + 



i 



5*^ 



E 



— 



— 



4+ 2ax 





.r + .rax ? 



G + 



2ax 



s 



n 



Ö 





— 



2ax 



7 + 



3ax 4 ? 





3ax + 



d 



o 



7 



— 



X+ ,rax 



8+ 2-4ax 





7+ 2- lax 



7 + 



2ax 



y 



a 



/? 



— 



2-3ax 8 + 



2ax 



8 + 



2-3ax 11 + 





2ax 12 + 



fi 



SS 



a 



jrax 



3ax 



2ax 





2ax 





2-3ax 



a 



<J 



— 



lax 



lax 



lax 





lax 





2ax 



— 







V 



IV 



III 



11 



l 





Proxiraal e n d s of axil-arms. 

 K. Sv. Vet. Aktul. Handl. Ban.l. 25. N:o 2. 



10 



