510 



Forty- fifth Report on the State Museum. 



Lingulasma, while in Trimerella and Dinobolus the platform is 

 deeply vaulted. The development of these platform vaults 

 does not proceed pari passu on both valves, but 

 appears first and is always the deeper on the 

 r pedicle-valve. The upper surface of the plat- 

 form always remains the area of muscular insertion, 

 and it seems highly probable that the vaults have 

 been formed by the necessity for the accommo- 

 dation of the great hepatic and genital glands; 



Fig. WO.—Rhinobolus 



Dawctoont. interior there can be little doubt, at least, that when 

 of pedicie-vaive these chambers are fully developed they are oceu- 



showing vaulted . _ , \\ . . .-, r. , 



platform. pied by these organs. A similar feature occurs in 



an aboloid genus, Lakhmina, and it is probable that among some 



of the articulate gen- 

 _ ^ x era wnere the ante- 

 W rior edge of the mus- 

 cular area is conspicu- 

 ously elevated (as fre- 

 quently in Lejjtama 

 rkomboidalis and 

 Prodtictus h u m e r - 

 os us) a similar cause 

 has been efficient. 

 Such structures are 

 not to be confounded 



Fig. 131.— Cardinal view of an internal cast of the pedicle - yH th excavations of 

 valve of Prorluctus humerosus; showing the filling of the great 

 median cavities or vaults, lying in front of the muscular scars, the Valves due to the 



(Davidson.) deposition of shell- 



matter about the ends of the muscles, leaving the scars of the latter 

 deeply sunk, as in many of the Spirifers. (Plates 23-28). 



Circulator v System. 

 The most striking and most distinctly specialized part of the cir- 

 culatory system is the series of canals which traverse the mantle, 

 lying within the tissue of the mantle itself. These canals consist 

 generally of two main trunks diverging from the anterior portion 

 of the pervisceral chamber and skirting themarginsof the visceral 

 area, giving oil secondary branches and ramuscules which arc 

 abundantly multiplied al the margins of the mantle. These pal- 

 Hal sinuses are frequently so highly developed as to modify the 

 inner surfaces of the valves,aml 1 races o\ them are often retained 



62 



