164 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. 50. 



31 ale 18 to 33 mm. long and 100 fi thick. The esophagus is G65 /a 

 long. The small bursa is short and rounded and only very slightly 

 incised dorsally (fig. 210). It is nearly transparent and readily 

 overlooked. The arrangement of the bursal rays is that given in the 

 generic diagnosis. The dorsal ray is 8 to 14 /* ( ? ) thick and has a slight 

 depression on its posterior border. The spicules are 160 to 170 [>. long. 

 They are flat, somewhat bent chitinous rods, somewhat broadened at 

 both ends, and the body of the spicules is marlvcd 

 with a distinct marbling (fig. 211). They are 

 provided with chitinous lateral lamellae in which 

 are chitinous rods, some simple and some distally 

 bifurcate, set at right angles 

 to the longitudinal axis of the 

 spicule. The rods are thicker 

 in the proximal portion of 

 the spicule and always end 

 bluntly. In the distal por- 

 tion of the spicule the lamel- 

 lae become wider and the 

 rods in them become thinner, 

 so that on the distal end they 

 are only appreciable on the 

 extruded spicule as very fine 

 lines on the thin lateral 

 lamellae. The lamellae are 

 directed toward one another 

 distally, but curve gradually 

 around the spicule proxi- 

 mally. A long retractor mus- 

 cle inserts in the proximal 

 swelling of the spicule and 

 proceeds anteriorly to its 

 origin in the cuticle of the lat- 

 eral body wall, while a more 

 complex muscle serves for the 

 extrusion of the spicule. With the spicules retracted, the unpaired 

 accessory structure lies between them in their distal ]3ortion. In its 

 general outline this structure is chevron-shaped, with the pomt of 

 the chevron directed anteriorly, and consists of six to eight sickle- 

 shaped chitinous structures projecting from a center and toothed on 

 the inner concave side. It is a fixed structure and occupies the same 

 position in the body regardless of whether the spicules are extruded 

 or retracted. The paired accessory structures are located in the 

 bursal region and are approximately parallel structures 33 fi long. 



ncr. 209.— Synthetocau- 



LU.S PULMONALIS. AN- 

 T Eli I OR EXTREMITY. 



Enlarged. After 

 Passerini, 1884. 



Fig. 210.— S-iTJJTHETOCAU- 

 LUS PULMONALIS. POS- 

 TERIOR EXTREMITY OF 



MALE. X 150. After 

 Railliet, 1893. 



