THE EXOGONEvE. 221 



EXOGONE HETEBOSETOSA, Mclnt. (Plate 17. figs. 11-17.) 



Exogone heterosetosa, Mcintosh, 20, p. 205, pi. 33. figs. 15 & 16 ; pi. 34 a, fig. 11. 

 Exogone heterosetosa, Mclnt., Ehlers, 8, p. 51, pi. 3. figs. 61-65. 

 ? Exogone heterosetosa, Mclnt., Gravier, 15. 

 Exogone heteroeh&ta, Mclnt., Angener, 1, p. 247. 



The specimens of this species which I have before me are all small worms, 

 not more than 4 mm. in length. There are about 40 segments. 



The palpi are elongated, longer than the prostominm and peristomium, 

 closely united, but separated distally by a distinct notch which is well marked 

 in late fixed embryos. The impaired tentacle extends as far as, or slightl)' 

 beyond, the extremity of the palpi. The lateral tentacles are not more than 

 half the length of the median. As regards the peristomial tentacles and the 

 dorsal cirri, there are two types. In the one all these appendages take the 

 form of stout cylinders. In the other they are all oval. The dorsal cirrus 

 of the second segment in all my specimens is absent. The ventral cirri are 

 smaller than the dorsad The anal cirri are long and tapering, similar in 

 shape and size to the median tentacle. 



Of the setae the most dorsally placed (PI. 17. fig. 12) is a simple, curved, 

 pointed form similar to the corresponding structure in E. fustifera. The next 

 (figs. 13 and 14) is a compound seta of a characteristic form. The shaft is 

 expanded at the end into a broad plate with an oblique, finely crenulated 

 edge. With this articulates the terminal appendage, which usually takes 

 the form of a very thin triangular plate sometimes replaced by a slender 

 tapering rod. The remaining compound setae (figs. 15 to 17), three or four 

 in number, are all similar to the corresponding setae of E. verrugera, with 

 small but well-formed appendages, or one may partake to some extent of the 

 special characters of that just described. Sexually mature specimens have 

 in addition bundles of capillary seta? on the segments from the twelfth or 

 thirteenth backwards. 



In the most complete specimens the proboscis is partly protracted and 

 the proventriculus lies in the 3rd, 4th, and 5th segments. In another, 

 apparently retracted, it lies in the 4th, 5th, and 6th. The proventriculus is 

 similar to that of E. verrugera, and has about 20 rows of muscle-columns. 



Augener refers to Exogone heterochwta, Mclnt. (obviously a slip for 

 E. heterosetosa) as one of the commonest species in South-west Australia 

 and states that his determination of the Australian specimens was confirmed 

 by comparison with southern-antarctic specimens. But I am not sure that 

 he has not confounded this species with the one which I have set down 

 tentatively as E. verrugera. 



In E. heterosetosa the presence of the notch between the palpi (which is well 

 shown in Mcintosh's original figure), and the absence of the dorsal cirri of 

 the second segment appear to be constant features (recognizable even in 



LINN. JOTJRN. — ZOOLOGY, VOL. XXXIV. 17 



