Fishes of the Western North Atlantic 333 



A single dorsal fin situated far forward on tail, or none. A well developed caudal fin 

 with radial supports in some but not in others. Outer margins of pelvics either straight 

 or convex.^ Spiracles with no trace of gill folds. 



Eyes and spiracles either on dorsal surface of head or on its sides. Apparent inner 

 (morphologically anterior) margins of nostrils united and expanded rearward as a 

 curtain, either simple or bilobed, the free posterior edge either smooth or fringed, 

 concealing all but outer end of nasal aperture. Teeth ranging from small and numerous 

 to large and few in number and compacted as a single grinding plate in each jaw. 



Skin of upper surface either naked or variously armed with tubercles or thorns, 

 the lower surface either naked or nearly so. Upper surface of tail with a large and saw- 

 edged poisonous spine (or spines) in many species but not in all. 



Anterior part of head supported either solely by anterior radial cartilages of pec- 

 toral fins or, in the case of the Devil Rays (Mobulidae), by the anterior contour of the 

 cranium, which is nearly straight transversely.^ Cranium without rostral projection; 

 antorbital cartilages not supporting part of disc. Fins without horny rays (ceratotrichia), 

 the cartilaginous radials extending out to margins of pectorals and pelvics, as well as 

 to margins of dorsal if present. Pelvis (Fig. 79) more or less strongly arched forward, 

 without prepelvic processes at outer ends and with or without a median process directed 

 forward. Surfaces of gill arches inward from gill filaments either smooth, or with papillae, 

 or with knobs or transverse folds or ridges (Fig. 80). 



Size. The members of this suborder range from only a few inches up to 22 or 

 23 feet in breadth and reach a weight of more than 3,000 pounds in the case of the 

 Giant Devil Rays {Mobula and Mantd), which are by far the largest of all batoids and 

 indeed among the largest of fishes. 



Developmental Stages. Ovoviviparous in all species in which development is known. 



Range. As a whole, the suborder is tropical-subtropical, only a few species ranging 

 regularly to warm-temperate latitudes. For the most part they are confined to small 

 and moderate depths and are most common in shallow water, where they are plentiful 

 in suitable situations around tropical shores. Many of them enter brackish and fresh 

 water freely, and one family of the order is confined to fresh water. 



Families. As seen in the list of names at the beginning of this section, the sub- 

 order includes a varied assemblage, all members of which agree in the characters 

 stated above. 



Key to Families 



I a. A well developed caudal fin with cartilaginous radial supports. 



, -, , 1 r Urolophidae.. p. 416. 



I b. No caudal fin. -^ ^ 



2 a. Outer anterior margins of pectorals continuous along sides of head, without 



separate cephalic fins or rostral lobes; eyes and spiracles on top of head. 



1. This contrasts with their usual concavity in the Rajoidea, as does the position of the dorsal fin. 



2. For a general account of the head skeleton in the families Dasyatidae and Myliobatidae, see Holmgren (.'\cta Zool. 

 Stockh., 22, 1941: 62, 66). 



