Sl'INKI) l.dACII. 



707 



character also aj)iieai-s with (■(}nsi(l('ral>lt' distinctness in 

 the compressed t'orni of the head, th(( thickness at tlie 

 eyes Ijeing less than " -, nt' tiie lengtii of tiie iiead", or 

 than ^4 of the lengtii of tlie base of tlie chirsal tin''. 

 The deep form of the snout is due to the mariad de- 

 velopment of the vertical plate of the ethmoid bone in 

 front of tlie nari'DW frontal bones, which are arched 

 above tlu^ orbits. The small round eyes are set liiyh 

 and turned somewiiat upwards, aliove the more or less 

 tumid cheeks, the distance between them and the upper 

 profile of the forehead beting about half their diameter'. 

 Their position is such that the length of the snout'' 

 (from their anterior inai'gin obliquely downwards to 

 its tip) is less than the postorbital length of the 

 head'' (from the posterior margin of the eyes ob- 

 liquely downwards to the hindmost part of the margin 

 of the liranchiostegal membi'ane). As in Mi^tiiiiims 

 fosslUs they are entirely covered with a thin skin 

 {ocuU rdati, Blkeker), the orbits being externally de- 

 stitute of any sharp limits. The anterior part of the 

 orbits is coasted below by a longitudinal slit in the 

 skin, out of which slit the fish can erect the preorbitid 

 spine, wliich otherwise points in a backward direction. 

 This sjiine is formed, as Lill.jebokg has pointed out, 

 bv the anterior frontal (lateral ethmoid) bone on each 

 side. This circumstance may be most easily elucidated 

 by a comj)arison with the folloAving species, where the 

 anterior frontal bone occupies exactly the same position 

 as the extended (vertical) base of the spine in this spe- 

 cies, forming the anterior margin of the orbit in a ver- 

 tical ])osition betwci'U the frontal and parasphenoid 

 biiiK's, Init with a firm o.sseous connexion (suture) with 

 the anterior outer margin of the orbitosjjhaMioideum, 

 which even sepai-ates the frontal bone proper from the 

 upper anterior corner of the triangular anterioi- frontal 

 bone. Here, in the Spined Loach, the said osseous 

 connexion is loose and transformed into an articulation. 

 The bone is also of much harder texture, white and 

 firm as dentine. Its base, wdiich forms the long, ver- 

 tical articulation with the orbitosphenoid bone, is almost 



terete and curved in a rounded obtuse angle, but is set 

 in a somewhat obliipie position, the lower (shorter) arm 

 of the angle running oblicpiely inwards and forwards, 

 while the upper arm is vertical. The tooth projects 

 backwards in a direction approaching to that of the 

 lower arm, at least below the middle of the basal part. 

 It is curved backwards and inwards and is generally 

 bicuspid, a shorter, but t(pially ])ointed tooth being set 

 at the middle of the outer surface of the main tocjth-''. 

 The base of the tooth is united by a strong ligament 

 to the hind margin of the orbit. The suborbital bones 

 seem otherwise to be entii-ely wanting both in this spe- 

 cies and JlLy/uniiis fossilis. In front of the preorbital 

 spine ;i dentiform protuberance belonging to the palatine 

 bone may be felt beneath the skin, at the iioint where 



Fig. 170. Riglit [ireorliilal spii)C of a Coliitis lania, seen from witliout. 

 Atioiil 15 times llie natural size. 



this bone is elongated in a backward direction to meet 

 the entopterj'goid bone. The nostrils are set rather high 

 on the sides of the snout, somewhat nearer to the eyes 

 than to the tip of the snout. The posterior nostril on 

 each side is round and somewhat larger than the anterior, 

 which lies just in front of it, and the hind superior 

 margin of which is canaliculate or elevated in an obli- 

 quely-cut, tubular form. The mouth is small and tooth- 

 less; it lies on the under surface of the head, fringed 

 by a comparatively thin upper lip, thickened only at 

 the corners of the mouth, and small bai-bels, which 

 comprise one pair in front and one on each side at the 

 middle of the u])per jaw, belonging to the dermal fold 

 that runs from the cheeks over the mouth and forms 

 the tip of the snout. The hindmost (largest) pair of 

 barbels, on the other hand, lie at the corners of the 



" 26 — 36 "4, according to mir nieasnrenieiits of speeiniens lietwcen ' n and 1 dm. long. Tlie greatest thickness of the liead measures, 

 according to Canesteini, 27 — 40 % of its length in the typical Vohiti.i tirnin; but in the form which has received the name of C. larcala, 

 it is said sometimes to measure 47 '^ »» thereof. 



' 48 — 69 %, according to our measurements. 



'■ The diameter of the eyes is about 20 — 15 "i of the length of the head. 



■' About 38— 4.B % of the length of the head. 



' About 49—56 'i of the length of the head. 



■' li. C. CedehstrOm (1. c.) has remarked as an external sexual difference that in the males the preorbital spine is furnished with 

 several lateral denticulatiiins. In the males cxauii7ied by us, however, this character does not hold good. 



