CRUSTACEA MALACOSTRACA. III. 123 



According to Sars' figures of the animals from above, /. hirticeps and /. denticulata differ ex- 

 tremely in the armature with spines on the anterior margins of the four anterior thoracic segments, 

 and must therefore be easy to separate. But the examination of a large material from numerous 

 places showed that / denticulata must be cancelled, as already stated by Ohlin (1901); I found spe- 

 cimens agreeing with /. hirticeps and others agreeing tolerably well with /. denticulata, but many 

 specimens showed intermediate features, and neither depth nor temperature at the bottom seems to be 

 of real influence on the development and character of the spines mentioned. Some particulars on the 

 variation may be of interest. 



The largest specimen, a female from the cold area ("Ingolf" Stat. 126, 293 fath.) is 10-5 mm. 

 long; it has nearly thirty spines, many among than moderately large, along the front margin of second 

 segment. A large specimen from Stat. 103 (579 fath., temp, -r- o - 6°) has about twenty-two spines on 

 the same margin, and in a small specimen, 3-4 mm. long, from the same station the marginal spines are 

 much less numerous, though very conspicuous. In a specimen 6-2 mm. long from Stat. 139 (702 fath., 

 temp, -f- o-6°) the spines on the margin of second segment are somewhat small and only twelve or fourteen, 

 while the head is almost smooth; in a smaller specimen 4-5 mm. long, from the same station, the head is 

 quite smooth and the marginal thoracic spines few and feebly developed. — My largest specimen from the 

 warm area, a female from Stat. 24 (1199 fath., temp. 2-4°), is 8 mm. long, has nearly thirty well developed 

 spines on the anterior margin of second segment, and is completely similar to large specimens from 

 the cold area; another female, 7 mm. long, from Stat. 24 has only sixteen or eighteen spines along 

 the same margin and several among them large; a third specimen, 4 mm. long, from the same station 

 has six large spines on the same margin. In specimens 6 — 7 mm. long from south of Iceland (L,at. 

 63°i5'N.) I find the anterior margin of the four segments extremely finely crenulate, the microscopic 

 teeth being more numerous than according to Sars figure of I. hirticeps, and, besides, set with a small 

 number of irregularly distributed, moderately strong spines, but probably some other spines have been 

 broken off; in specimens 4-5 — 5 mm. long from the same place the fine crenulation is well developed, 

 but no real spines are found, while the head has as usual numerous spines. In specimens 6 — 7 mm. 

 long from another place in the warm area, viz. south-west of the Faeroes in L,at. 6i°i5' N., the fine 

 crenulation is very distinct, but scarcely any spine could be detected on the margins. — In very juve- 

 nile specimens, from 2-5 to 3 mm. or rarely nearly 4 mm., the spines on the head and spines or crenu- 

 lation on the margins of the four anterior segments are sometimes partly or totally undeveloped. 



All specimens, excepting the most juvenile, are distinguished from /. dubia n. sp. in having 

 the head conspicuously broader than first segment, about as broad as, or frequently broader than, se- 

 cond thoracic segment. /. hirticeps is separated from / longicomis G. O. S. (= I. Plwiketti Tatt.) in 

 having the basal joint of the antennulse (fig. 7 a) armed with a few or several spines on the outer 

 margin, and, besides, this joint is proportionately longer than in /. longicomis. (Above, on p. 121, it has 

 been mentioned that in Sars' main figure of /. denticulata the basal joint of the antennulse is correct, 

 while it is wrong in his figures of /. longicomis and /. hirticeps.) Of /. longicomis one of the largest 

 specimens is 47 mm., thus considerably larger than according to Sars, who said "'about 3 mm."; 

 adult specimens of this species are rather similar to specimens of the same size of / hirticeps, but can 



be distinguished by first antennular joint and by having no spines on the head and no vestige of 



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