﻿90 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 102 



CIRCULATORY SYSTEM 

 FlGUBE 38 



The small saclike pericardium is situated at the posterior end of 

 the ctenidium in the region between the kidney and the lower stomach, 

 or crystalline style sac. There is one auricle and posterior to it a 

 single, smaller ventricle. The auricle is round and bulbous, with thin 

 walls. In preserved material, "jellied" blood fills this organ. At its 

 anterior end the large, efferent ctenidial vessel enters. At its pos- 

 terior end it joins the ventricle. The ventricle is somewhat triangular 

 with its broad base appressed to the auricle. It is relatively thick 

 walled with a large number of separate, long muscle fibers running 

 crisscross over the inner surface. Many of these fibers join at the 

 anterior end to form a round valve, which prevents blood from revers- 

 ing its course. On the ventral surface at the apical end of the ventricle 

 there is another slitlike valve. At this point the blood enters the thin- 

 walled transparent truncus arteriosus, which soon divides into an 

 anterior and a posterior, or visceral, artery. The latter is round in 

 cross-section in living material but collapses in preserved specimens. 

 It runs posteriorly, first giving off a short artery to the left, which 

 supplies the region of the crystalline style sac. It proceeds farther 

 toward the apical whorls in close proximity to the stomach and then 

 proceeds anteriorly to supply the anterior region of the foot and body. 



The venous system has not been followed adequately in this species 

 because of the difficulties in following the numerous sinuses. It ap- 

 pears that the sinuses that bathe the various organs are ill defined and 

 have complex interconnections. The rectal sinus is the most easily 

 found, and it is situated in the region of the lower part of the kidney 

 and the intestine. The blood flows from this largest sinus into the 

 ctenidial lamellae. Small sinuses have been noted in the region of the 

 pedal ganglia, digestive gland, esophagus, and stomach. The complex 

 of sinuses noted in the mantle of Palvdomus by Seshaiya (1934) are 

 similar, but are more highly developed than in Thiara granifera. 



The bluish-green color of the mantle and other parts of the internal 

 organs noted by Seshaiya (1934) is conunon not only to Paludomus 

 and Thiara but also to a number of New World members of the Thiar- 

 idae. Seshaiya suggests that this is due to the presence of haemocy- 

 anin in the blood. 



The ctenidium is long and narrow and is welded to the mantle. It 

 extends from the apex of the mantle cavity in the region of the heart 

 forward almost to the mantle edge. It bears approximately 190 to 200 

 separate gill lamellae, which are triangular, and which hang with 

 their apices facing downward into the mantle cavity. 



