120 "terra nova" expedition. 



Order HETERONEMERTINI. 

 Fam. BASEODISCID.^1 



Jiasfudisciis, Diesiiiij,'. 1S50. [= /•^ii/hi/Ih. ] luln'cclit, 1887.] 

 4. jHi'^i'inlisciis iiiitdriiiciis, sp. u. (I'l. 1. tigs. 4. G.) 

 Stations .".14 aiid ;">55 : McMurdo Sound, 222-300 fathoms. 



A fairly distiiK-t c-diistrictioii iiuinediately behind the mouth, when tlie heud is not reti'acted. 

 Cephalic grooves lateral and vertical. Mouth small and circular. Primary basement-menilirane of cutis 

 deep, hut loose, and with manj- radial muscle-fibres. A well-developed layer of gland-cells in connection 

 with the cutis. Bundles of fibres in outer longitudinal muscle-layer of body separated by uuich g(4atiiious 

 tissue. Circular muscle-layer thin. AValls of gut not folded. Proboscis slender, and prolioscis-shcath 

 thin-walled. 



Two specimens wliidi 1 refer to tliis foim occur in the collection. 



The larger of the two measures 5 • ,5 cm. in length, and has a maximum thickness 

 of 9 mm. The smaller, whicli is apparently a young female, measures onl\- 2 cm. in 

 length and .") mm. in thickness. 



There is no trace of colour <n- mai'kings upon either individual. 



External Features. 



In the small specimen the characters of the hea-d (PI. 1, tig. 4) can he fairly well made 

 out ; it is marked off from the bodv by a moderately distinct constriction, immediately 

 behind the mouth. The prohoscis-pore (L'.P.) is a well-marked vertical slit just lielow 

 the apex of the head. The shallow cephalic grooves (G.) are lateral and vertical, and 

 apparentlv do not form a complete ring. The mouth (M.) is snudl and circular, with 

 resularlv wrinkled maro'iu. 



In the larger example the head is inuch retracted, and little of these features i-an 

 lie made out with certainty. 



Internal Anatomy. 



A .small piece was taken from about the middle of the body of the small specimen, 

 and cut into transverse sections (PI. I, fig. (i). These reveal the following features : — 



The external epithelium of the body (Ep.) consi.sts of tall cells, resting on a 

 secoD(hirv l>asemeut-meml:)rane (B.M".), succeeded by two thin layers of mu.st-le-tibres. 

 an outer circular and an inner longitudinal. Beneath the latter is a well-developed 

 layer (Ul.) of large glandular cells. Next comes the thick jirinniry basement- 

 membrane (B.]\P.). consisting of a rather loose connective tissue, through which many 

 bundles of muscle-fibres pass outward radially. 



The outer laver of longitudinal body-nniscles ([..Ml) cunu's next in order. The 



