loiia 



of \V(irk \\lii<'li he ;issio-|icd on the one liniul to the aiu- 

 pulhi' as S('ci'i't()i'\' organs, on tlie oflicr to the hiteriil 

 hue proper and tlie Savian vesicles as organs of sense, 

 n'i|nires fnrtlier denionstration. Its anatomical structnre 

 ranges the s^■stenl of tlie lateral line witii all its niodi- 

 fications as intermediate between the organs of iiearing 

 and those of the senses of jiressure (tonch — especially 

 as in the worms), taste, and smell; and its physiological 

 significance is perhaps best expressed as yet by Ley- 

 pig's assnniption tliat it apjiertains to a sixtii sense, 

 foreign to ns, and receptivt' of the impressions yielded 

 h\- siu-h \ ilirations of the surrounding medium as are too 

 grave (slow) for appreciation by the organs of hearing. 

 The Rays probably spend the greater ])art of their 

 existence in a stationarv jiosition at the bottom, and to 

 facilitate their i espiiMtion, to keep the gill-slits supj)lied 

 witli IVesh water, thcv have been provided with large 

 spiracles on the upper side of the head, just liehind the 

 eyes. Above each spiracle is simple, below the passage 

 divides into two, one l)ranc]i entering the cavitv of the 

 mouth, the other passing to the gills. To prevent the 

 water thus supplied from escaping through the mouth, 

 the\' Ikinc a palatal fold, usually of jxnverful develop- 

 ment, in the upper jnw. On the under surface of the 

 head the nasal cavities show about the same relation 

 to the mouth-ca\ity as in the Hohccpliali, only tliat no 

 lateral uppei' lip encloses them outside and in front. 

 Here tlie median upper lij) instead is still more deve- 

 Idiied. and forms a broad dermal fold extendinu' fi'om 



tlie aiiiei'ioi' margins of the nostrils and betw<H'n them 

 back to the cornei-s of tlie mouth", on each side cover- 

 ing a deep groove that runs irom the nasal cavit}* to 

 the corner of the moutli. Hu tiie outside this groove 

 is bounded b\- a dermal i-idge, which is indeed furnished 

 anteriorh' with a more or less prominent, Idunt or 

 rather jiointed proluberaiice, l)Ut which does not form 

 any limit between tlie anterior and ])Osterior nostrils. 

 The fi\(' |)airs of liranchial apertures are set on the 

 ventral side'', in two more or less straight lines con- 

 verging beldnd or in a eur\e anteriorly concave, pos- 

 teriorh' interrupted, belniid tlie head and between the 

 prorsal jiarts of the pectoral fins. 



.\s the form-series of the Rays, winch includes 

 about a hundred and tifty species, is a develoiimental 

 offshoot of the Selachian type, the forms that have most 

 widely diverged from the Sharks must, of course, be 

 regarded as the most advanced in the scale of evolution. 

 Among the Rays observed in Scandinavia there are two 

 families which are both distinguished by the exceedingly 

 slender (whip-like) tail and by the loss of at least one 

 dorsal tin. In tlie tliird family of Scandinavian Hays 

 both dorsal fins are jiersistent on the much l)roader and 

 depressed tail, which is besides fringed on the sides 

 with a more or less distinct dermal fold. But e\en 

 this family is more \videly remo\ed from the Selachian 

 type than the three remaining families, which are 

 strangers to our fauna: the Tofpcdhtidte, lihiiiohatidcc, 

 and Prisfi(hr. 



Fa M MYLIOBATID.E. 



The irliiji-lili' tail iriflioiif cuuilal fin, but ir'ith n ihirsal fin in front, lirhind irliirh there (/enertilli/ appears a 



serrated spiiw, n-ith or witliout eonipensator// spine. Tlie Jarfie peeforal fins interrujited on the sides of the head, 



bat continaed on the sides of the siiont bij so-eaJJed eephaJic fins. 



This family contains the giants among the Rays, 

 some forms l)eing veritable monsters of the deep. In 

 addition to the characters given above the members of 

 the family are distinguished b^• the elevation of the 

 head above tlie plane of the pectoral tins, the forehead 

 being especially high, and causing the eyes to assume 

 a vertical jiosition with lateral aspect, instead of the 



oblique or horizontal jiosition the^" occujiv in the other 

 Raj-s. The skin too is smooth during youth in most 

 of these fishes, and in older sjjecimens is commonh- 

 shagi'eened on the tail alone or also on the bases of 

 the pectoral fins, but sometimes over the whole body. 

 The family derives its uiime from the form and molar 

 function of the jaw-teeth, which are adajjted fVir the 



" The abovc-meiilioneJ intermediate forms (tlic Kliinoliatido! and Piintkhe) between tlie Rays and Sharks are approximated to tlie 

 Sharks in this respect too, and have the nostrils entirely separated from the mouth. 



' Hence the name of Hi/potvemes, applied by DCmerii. to the suborder of the Rays. 



